diff --git a/crates/handlers/src/admin/v1/mod.rs b/crates/handlers/src/admin/v1/mod.rs
index 1fb11dec8..31d28c155 100644
--- a/crates/handlers/src/admin/v1/mod.rs
+++ b/crates/handlers/src/admin/v1/mod.rs
@@ -26,6 +26,7 @@ mod user_emails;
 mod user_sessions;
 mod users;
 
+#[allow(clippy::too_many_lines)]
 pub fn router<S>() -> ApiRouter<S>
 where
     S: Clone + Send + Sync + 'static,
@@ -123,6 +124,10 @@ where
             get_with(
                 self::upstream_oauth_links::list,
                 self::upstream_oauth_links::list_doc,
+            )
+            .post_with(
+                self::upstream_oauth_links::add,
+                self::upstream_oauth_links::add_doc,
             ),
         )
         .api_route(
diff --git a/crates/handlers/src/admin/v1/upstream_oauth_links/add.rs b/crates/handlers/src/admin/v1/upstream_oauth_links/add.rs
new file mode 100644
index 000000000..867a5e557
--- /dev/null
+++ b/crates/handlers/src/admin/v1/upstream_oauth_links/add.rs
@@ -0,0 +1,368 @@
+// Copyright 2025 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only
+// Please see LICENSE in the repository root for full details.
+
+use aide::{NoApi, OperationIo, transform::TransformOperation};
+use axum::{Json, response::IntoResponse};
+use hyper::StatusCode;
+use mas_storage::{BoxRng, upstream_oauth2::UpstreamOAuthLinkFilter};
+use schemars::JsonSchema;
+use serde::Deserialize;
+use ulid::Ulid;
+
+use crate::{
+    admin::{
+        call_context::CallContext,
+        model::{Resource, UpstreamOAuthLink, User},
+        response::{ErrorResponse, SingleResponse},
+    },
+    impl_from_error_for_route,
+};
+
+#[derive(Debug, thiserror::Error, OperationIo)]
+#[aide(output_with = "Json<ErrorResponse>")]
+pub enum RouteError {
+    #[error(transparent)]
+    Internal(Box<dyn std::error::Error + Send + Sync + 'static>),
+
+    #[error("User ID {0} already has an upstream link for Upstream Oauth 2.0 Provider ID {1}")]
+    LinkAlreadyExists(Ulid, Ulid),
+
+    #[error("User ID {0} not found")]
+    UserNotFound(Ulid),
+
+    #[error("Upstream OAuth 2.0 Provider ID {0} not found")]
+    ProviderNotFound(Ulid),
+}
+
+impl_from_error_for_route!(mas_storage::RepositoryError);
+
+impl IntoResponse for RouteError {
+    fn into_response(self) -> axum::response::Response {
+        let error = ErrorResponse::from_error(&self);
+        let status = match self {
+            Self::Internal(_) => StatusCode::INTERNAL_SERVER_ERROR,
+            Self::LinkAlreadyExists(_, _) => StatusCode::CONFLICT,
+            Self::UserNotFound(_) | Self::ProviderNotFound(_) => StatusCode::NOT_FOUND,
+        };
+        (status, Json(error)).into_response()
+    }
+}
+
+/// # JSON payload for the `POST /api/admin/v1/upstream-oauth-links`
+#[derive(Deserialize, JsonSchema)]
+#[serde(rename = "AddUpstreamOauthLinkRequest")]
+pub struct Request {
+    /// The ID of the user to which the link should be added.
+    #[schemars(with = "crate::admin::schema::Ulid")]
+    user_id: Ulid,
+
+    /// The ID of the upstream provider to which the link is for.
+    #[schemars(with = "crate::admin::schema::Ulid")]
+    provider_id: Ulid,
+
+    /// The subject (sub) claim of the user on the provider.
+    subject: String,
+
+    /// A human readable account name.
+    human_account_name: Option<String>,
+}
+
+pub fn doc(operation: TransformOperation) -> TransformOperation {
+    operation
+        .id("addUpstreamOAuthLink")
+        .summary("Add an upstream OAuth 2.0 link")
+        .tag("upstream-oauth-link")
+        .response_with::<201, Json<SingleResponse<UpstreamOAuthLink>>, _>(|t| {
+            let [sample, ..] = UpstreamOAuthLink::samples();
+            let response = SingleResponse::new_canonical(sample);
+            t.description("Upstream OAuth 2.0 link was created")
+                .example(response)
+        })
+        .response_with::<409, RouteError, _>(|t| {
+            let [provider_sample, ..] = UpstreamOAuthLink::samples();
+            let [user_sample, ..] = User::samples();
+            let response = ErrorResponse::from_error(&RouteError::LinkAlreadyExists(
+                user_sample.id(),
+                provider_sample.id(),
+            ));
+            t.description("User already has an upstream link for this provider")
+                .example(response)
+        })
+        .response_with::<404, RouteError, _>(|t| {
+            let response = ErrorResponse::from_error(&RouteError::UserNotFound(Ulid::nil()));
+            t.description("User or provider was not found")
+                .example(response)
+        })
+}
+
+#[tracing::instrument(name = "handler.admin.v1.upstream_oauth_links.post", skip_all, err)]
+pub async fn handler(
+    CallContext {
+        mut repo, clock, ..
+    }: CallContext,
+    NoApi(mut rng): NoApi<BoxRng>,
+    Json(params): Json<Request>,
+) -> Result<(StatusCode, Json<SingleResponse<UpstreamOAuthLink>>), RouteError> {
+    // Find the user
+    let user = repo
+        .user()
+        .lookup(params.user_id)
+        .await?
+        .ok_or(RouteError::UserNotFound(params.user_id))?;
+
+    // Find the provider
+    let provider = repo
+        .upstream_oauth_provider()
+        .lookup(params.provider_id)
+        .await?
+        .ok_or(RouteError::ProviderNotFound(params.provider_id))?;
+
+    let filter = UpstreamOAuthLinkFilter::new()
+        .for_user(&user)
+        .for_provider(&provider);
+    let count = repo.upstream_oauth_link().count(filter).await?;
+
+    if count > 0 {
+        return Err(RouteError::LinkAlreadyExists(
+            params.user_id,
+            params.provider_id,
+        ));
+    }
+
+    let mut link = repo
+        .upstream_oauth_link()
+        .add(
+            &mut rng,
+            &clock,
+            &provider,
+            params.subject,
+            params.human_account_name,
+        )
+        .await?;
+
+    repo.upstream_oauth_link()
+        .associate_to_user(&link, &user)
+        .await?;
+    link.user_id = Some(user.id);
+
+    repo.save().await?;
+
+    Ok((
+        StatusCode::CREATED,
+        Json(SingleResponse::new_canonical(link.into())),
+    ))
+}
+
+#[cfg(test)]
+mod tests {
+    use hyper::{Request, StatusCode};
+    use insta::assert_json_snapshot;
+    use sqlx::PgPool;
+    use ulid::Ulid;
+
+    use super::super::test_utils;
+    use crate::test_utils::{RequestBuilderExt, ResponseExt, TestState, setup};
+
+    #[sqlx::test(migrator = "mas_storage_pg::MIGRATOR")]
+    async fn test_create(pool: PgPool) {
+        setup();
+        let mut state = TestState::from_pool(pool).await.unwrap();
+        let token = state.token_with_scope("urn:mas:admin").await;
+        let mut rng = state.rng();
+        let mut repo = state.repository().await.unwrap();
+
+        let alice = repo
+            .user()
+            .add(&mut rng, &state.clock, "alice".to_owned())
+            .await
+            .unwrap();
+
+        let provider = repo
+            .upstream_oauth_provider()
+            .add(
+                &mut rng,
+                &state.clock,
+                test_utils::oidc_provider_params("provider1"),
+            )
+            .await
+            .unwrap();
+
+        repo.save().await.unwrap();
+
+        let request = Request::post("/api/admin/v1/upstream-oauth-links")
+            .bearer(&token)
+            .json(serde_json::json!({
+                "user_id": alice.id,
+                "provider_id": provider.id,
+                "subject": "subject1"
+            }));
+        let response = state.request(request).await;
+        response.assert_status(StatusCode::CREATED);
+        let body: serde_json::Value = response.json();
+        assert_json_snapshot!(body, @r###"
+        {
+          "data": {
+            "type": "upstream-oauth-link",
+            "id": "01FSHN9AG07HNEZXNQM2KNBNF6",
+            "attributes": {
+              "created_at": "2022-01-16T14:40:00Z",
+              "provider_id": "01FSHN9AG0AJ6AC5HQ9X6H4RP4",
+              "subject": "subject1",
+              "user_id": "01FSHN9AG0MZAA6S4AF7CTV32E",
+              "human_account_name": null
+            },
+            "links": {
+              "self": "/api/admin/v1/upstream-oauth-links/01FSHN9AG07HNEZXNQM2KNBNF6"
+            }
+          },
+          "links": {
+            "self": "/api/admin/v1/upstream-oauth-links/01FSHN9AG07HNEZXNQM2KNBNF6"
+          }
+        }
+        "###);
+    }
+
+    #[sqlx::test(migrator = "mas_storage_pg::MIGRATOR")]
+    async fn test_link_already_exists(pool: PgPool) {
+        setup();
+        let mut state = TestState::from_pool(pool).await.unwrap();
+        let token = state.token_with_scope("urn:mas:admin").await;
+        let mut rng = state.rng();
+        let mut repo = state.repository().await.unwrap();
+
+        let alice = repo
+            .user()
+            .add(&mut rng, &state.clock, "alice".to_owned())
+            .await
+            .unwrap();
+
+        let provider = repo
+            .upstream_oauth_provider()
+            .add(
+                &mut rng,
+                &state.clock,
+                test_utils::oidc_provider_params("provider1"),
+            )
+            .await
+            .unwrap();
+
+        let link = repo
+            .upstream_oauth_link()
+            .add(
+                &mut rng,
+                &state.clock,
+                &provider,
+                String::from("subject1"),
+                None,
+            )
+            .await
+            .unwrap();
+
+        repo.upstream_oauth_link()
+            .associate_to_user(&link, &alice)
+            .await
+            .unwrap();
+
+        repo.save().await.unwrap();
+
+        let request = Request::post("/api/admin/v1/upstream-oauth-links")
+            .bearer(&token)
+            .json(serde_json::json!({
+                "user_id": alice.id,
+                "provider_id": provider.id,
+                "subject": "subject1"
+            }));
+        let response = state.request(request).await;
+        response.assert_status(StatusCode::CONFLICT);
+        let body: serde_json::Value = response.json();
+        assert_json_snapshot!(body, @r###"
+        {
+          "errors": [
+            {
+              "title": "User ID 01FSHN9AG0MZAA6S4AF7CTV32E already has an upstream link for Upstream Oauth 2.0 Provider ID 01FSHN9AG0AJ6AC5HQ9X6H4RP4"
+            }
+          ]
+        }
+        "###);
+    }
+
+    #[sqlx::test(migrator = "mas_storage_pg::MIGRATOR")]
+    async fn test_user_not_found(pool: PgPool) {
+        setup();
+        let mut state = TestState::from_pool(pool).await.unwrap();
+        let token = state.token_with_scope("urn:mas:admin").await;
+        let mut rng = state.rng();
+        let mut repo = state.repository().await.unwrap();
+
+        let provider = repo
+            .upstream_oauth_provider()
+            .add(
+                &mut rng,
+                &state.clock,
+                test_utils::oidc_provider_params("provider1"),
+            )
+            .await
+            .unwrap();
+
+        repo.save().await.unwrap();
+
+        let request = Request::post("/api/admin/v1/upstream-oauth-links")
+            .bearer(&token)
+            .json(serde_json::json!({
+                "user_id": Ulid::nil(),
+                "provider_id": provider.id,
+                "subject": "subject1"
+            }));
+        let response = state.request(request).await;
+        response.assert_status(StatusCode::NOT_FOUND);
+        let body: serde_json::Value = response.json();
+        assert_json_snapshot!(body, @r###"
+        {
+          "errors": [
+            {
+              "title": "User ID 00000000000000000000000000 not found"
+            }
+          ]
+        }
+        "###);
+    }
+
+    #[sqlx::test(migrator = "mas_storage_pg::MIGRATOR")]
+    async fn test_provider_not_found(pool: PgPool) {
+        setup();
+        let mut state = TestState::from_pool(pool).await.unwrap();
+        let token = state.token_with_scope("urn:mas:admin").await;
+        let mut rng = state.rng();
+        let mut repo = state.repository().await.unwrap();
+
+        let alice = repo
+            .user()
+            .add(&mut rng, &state.clock, "alice".to_owned())
+            .await
+            .unwrap();
+
+        repo.save().await.unwrap();
+
+        let request = Request::post("/api/admin/v1/upstream-oauth-links")
+            .bearer(&token)
+            .json(serde_json::json!({
+                "user_id": alice.id,
+                "provider_id": Ulid::nil(),
+                "subject": "subject1"
+            }));
+        let response = state.request(request).await;
+        response.assert_status(StatusCode::NOT_FOUND);
+        let body: serde_json::Value = response.json();
+        assert_json_snapshot!(body, @r###"
+        {
+          "errors": [
+            {
+              "title": "Upstream OAuth 2.0 Provider ID 00000000000000000000000000 not found"
+            }
+          ]
+        }
+        "###);
+    }
+}
diff --git a/crates/handlers/src/admin/v1/upstream_oauth_links/mod.rs b/crates/handlers/src/admin/v1/upstream_oauth_links/mod.rs
index e6dcdd22d..09203c3d1 100644
--- a/crates/handlers/src/admin/v1/upstream_oauth_links/mod.rs
+++ b/crates/handlers/src/admin/v1/upstream_oauth_links/mod.rs
@@ -3,10 +3,12 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 // Please see LICENSE in the repository root for full details.
 
+mod add;
 mod get;
 mod list;
 
 pub use self::{
+    add::{doc as add_doc, handler as add},
     get::{doc as get_doc, handler as get},
     list::{doc as list_doc, handler as list},
 };
diff --git a/docs/api/spec.json b/docs/api/spec.json
index d14b2c3f8..eb52d07ba 100644
--- a/docs/api/spec.json
+++ b/docs/api/spec.json
@@ -2289,6 +2289,88 @@
             }
           }
         }
+      },
+      "post": {
+        "tags": [
+          "upstream-oauth-link"
+        ],
+        "summary": "Add an upstream OAuth 2.0 link",
+        "operationId": "addUpstreamOAuthLink",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/AddUpstreamOauthLinkRequest"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "201": {
+            "description": "Upstream OAuth 2.0 link was created",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/SingleResponse_for_UpstreamOAuthLink"
+                },
+                "example": {
+                  "data": {
+                    "type": "upstream-oauth-link",
+                    "id": "01040G2081040G2081040G2081",
+                    "attributes": {
+                      "created_at": "1970-01-01T00:00:00Z",
+                      "provider_id": "02081040G2081040G2081040G2",
+                      "subject": "john-42",
+                      "user_id": "030C1G60R30C1G60R30C1G60R3",
+                      "human_account_name": "john.doe@example.com"
+                    },
+                    "links": {
+                      "self": "/api/admin/v1/upstream-oauth-links/01040G2081040G2081040G2081"
+                    }
+                  },
+                  "links": {
+                    "self": "/api/admin/v1/upstream-oauth-links/01040G2081040G2081040G2081"
+                  }
+                }
+              }
+            }
+          },
+          "409": {
+            "description": "User already has an upstream link for this provider",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                },
+                "example": {
+                  "errors": [
+                    {
+                      "title": "User ID 01040G2081040G2081040G2081 already has an upstream link for Upstream Oauth 2.0 Provider ID 01040G2081040G2081040G2081"
+                    }
+                  ]
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "User or provider was not found",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ErrorResponse"
+                },
+                "example": {
+                  "errors": [
+                    {
+                      "title": "User ID 00000000000000000000000000 not found"
+                    }
+                  ]
+                }
+              }
+            }
+          }
+        }
       }
     },
     "/api/admin/v1/upstream-oauth-links/{id}": {
@@ -3504,6 +3586,34 @@
           }
         }
       },
+      "AddUpstreamOauthLinkRequest": {
+        "title": "JSON payload for the `POST /api/admin/v1/upstream-oauth-links`",
+        "type": "object",
+        "required": [
+          "provider_id",
+          "subject",
+          "user_id"
+        ],
+        "properties": {
+          "user_id": {
+            "description": "The ID of the user to which the link should be added.",
+            "$ref": "#/components/schemas/ULID"
+          },
+          "provider_id": {
+            "description": "The ID of the upstream provider to which the link is for.",
+            "$ref": "#/components/schemas/ULID"
+          },
+          "subject": {
+            "description": "The subject (sub) claim of the user on the provider.",
+            "type": "string"
+          },
+          "human_account_name": {
+            "description": "A human readable account name.",
+            "type": "string",
+            "nullable": true
+          }
+        }
+      },
       "SingleResponse_for_UpstreamOAuthLink": {
         "description": "A top-level response with a single resource",
         "type": "object",