diff --git a/.buildkite/.env b/.buildkite/.env
deleted file mode 100644
index 85b102d07..000000000
--- a/.buildkite/.env
+++ /dev/null
@@ -1,13 +0,0 @@
-CI
-BUILDKITE
-BUILDKITE_BUILD_NUMBER
-BUILDKITE_BRANCH
-BUILDKITE_BUILD_NUMBER
-BUILDKITE_JOB_ID
-BUILDKITE_BUILD_URL
-BUILDKITE_PROJECT_SLUG
-BUILDKITE_COMMIT
-BUILDKITE_PULL_REQUEST
-BUILDKITE_TAG
-CODECOV_TOKEN
-TRIAL_FLAGS
diff --git a/.buildkite/merge_base_branch.sh b/.buildkite/merge_base_branch.sh
deleted file mode 100755
index 361440fd1..000000000
--- a/.buildkite/merge_base_branch.sh
+++ /dev/null
@@ -1,35 +0,0 @@
-#!/usr/bin/env bash
-
-set -e
-
-if [[ "$BUILDKITE_BRANCH" =~ ^(develop|master|dinsic|shhs|release-.*)$ ]]; then
-    echo "Not merging forward, as this is a release branch"
-    exit 0
-fi
-
-if [[ -z $BUILDKITE_PULL_REQUEST_BASE_BRANCH ]]; then
-    echo "Not a pull request, or hasn't had a PR opened yet..."
-
-    # It probably hasn't had a PR opened yet. Since all PRs land on develop, we
-    # can probably assume it's based on it and will be merged into it.
-    GITBASE="develop"
-else
-    # Get the reference, using the GitHub API
-    GITBASE=$BUILDKITE_PULL_REQUEST_BASE_BRANCH
-fi
-
-echo "--- merge_base_branch $GITBASE"
-
-# Show what we are before
-git --no-pager show -s
-
-# Set up username so it can do a merge
-git config --global user.email bot@matrix.org
-git config --global user.name "A robot"
-
-# Fetch and merge. If it doesn't work, it will raise due to set -e.
-git fetch -u origin $GITBASE
-git merge --no-edit --no-commit origin/$GITBASE
-
-# Show what we are after.
-git --no-pager show -s
diff --git a/.buildkite/postgres-config.yaml b/.ci/postgres-config.yaml
similarity index 86%
rename from .buildkite/postgres-config.yaml
rename to .ci/postgres-config.yaml
index 67e17fa9d..f5a4aecd5 100644
--- a/.buildkite/postgres-config.yaml
+++ b/.ci/postgres-config.yaml
@@ -3,7 +3,7 @@
 # CI's Docker setup at the point where this file is considered.
 server_name: "localhost:8800"
 
-signing_key_path: ".buildkite/test.signing.key"
+signing_key_path: ".ci/test.signing.key"
 
 report_stats: false
 
@@ -11,7 +11,7 @@ database:
   name: "psycopg2"
   args:
     user: postgres
-    host: postgres
+    host: localhost
     password: postgres
     database: synapse
 
diff --git a/.buildkite/scripts/postgres_exec.py b/.ci/scripts/postgres_exec.py
similarity index 92%
rename from .buildkite/scripts/postgres_exec.py
rename to .ci/scripts/postgres_exec.py
index 086b39172..0f39a336d 100755
--- a/.buildkite/scripts/postgres_exec.py
+++ b/.ci/scripts/postgres_exec.py
@@ -23,7 +23,7 @@ import psycopg2
 # We use "postgres" as a database because it's bound to exist and the "synapse" one
 # doesn't exist yet.
 db_conn = psycopg2.connect(
-    user="postgres", host="postgres", password="postgres", dbname="postgres"
+    user="postgres", host="localhost", password="postgres", dbname="postgres"
 )
 db_conn.autocommit = True
 cur = db_conn.cursor()
diff --git a/.buildkite/scripts/test_old_deps.sh b/.ci/scripts/test_old_deps.sh
similarity index 81%
rename from .buildkite/scripts/test_old_deps.sh
rename to .ci/scripts/test_old_deps.sh
index 9270d55f0..8b473936f 100755
--- a/.buildkite/scripts/test_old_deps.sh
+++ b/.ci/scripts/test_old_deps.sh
@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-# this script is run by buildkite in a plain `bionic` container; it installs the
+# this script is run by GitHub Actions in a plain `bionic` container; it installs the
 # minimal requirements for tox and hands over to the py3-old tox environment.
 
 set -ex
diff --git a/.buildkite/scripts/test_synapse_port_db.sh b/.ci/scripts/test_synapse_port_db.sh
similarity index 60%
rename from .buildkite/scripts/test_synapse_port_db.sh
rename to .ci/scripts/test_synapse_port_db.sh
index 82d7d56d4..2b4e5ec17 100755
--- a/.buildkite/scripts/test_synapse_port_db.sh
+++ b/.ci/scripts/test_synapse_port_db.sh
@@ -20,22 +20,22 @@ pip install -e .
 echo "--- Generate the signing key"
 
 # Generate the server's signing key.
-python -m synapse.app.homeserver --generate-keys -c .buildkite/sqlite-config.yaml
+python -m synapse.app.homeserver --generate-keys -c .ci/sqlite-config.yaml
 
 echo "--- Prepare test database"
 
 # Make sure the SQLite3 database is using the latest schema and has no pending background update.
-scripts-dev/update_database --database-config .buildkite/sqlite-config.yaml
+scripts-dev/update_database --database-config .ci/sqlite-config.yaml
 
 # Create the PostgreSQL database.
-./.buildkite/scripts/postgres_exec.py "CREATE DATABASE synapse"
+.ci/scripts/postgres_exec.py "CREATE DATABASE synapse"
 
 echo "+++ Run synapse_port_db against test database"
-coverage run scripts/synapse_port_db --sqlite-database .buildkite/test_db.db --postgres-config .buildkite/postgres-config.yaml
+coverage run scripts/synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
 
 # We should be able to run twice against the same database.
 echo "+++ Run synapse_port_db a second time"
-coverage run scripts/synapse_port_db --sqlite-database .buildkite/test_db.db --postgres-config .buildkite/postgres-config.yaml
+coverage run scripts/synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
 
 #####
 
@@ -44,14 +44,14 @@ coverage run scripts/synapse_port_db --sqlite-database .buildkite/test_db.db --p
 echo "--- Prepare empty SQLite database"
 
 # we do this by deleting the sqlite db, and then doing the same again.
-rm .buildkite/test_db.db
+rm .ci/test_db.db
 
-scripts-dev/update_database --database-config .buildkite/sqlite-config.yaml
+scripts-dev/update_database --database-config .ci/sqlite-config.yaml
 
 # re-create the PostgreSQL database.
-./.buildkite/scripts/postgres_exec.py \
+.ci/scripts/postgres_exec.py \
   "DROP DATABASE synapse" \
   "CREATE DATABASE synapse"
 
 echo "+++ Run synapse_port_db against empty database"
-coverage run scripts/synapse_port_db --sqlite-database .buildkite/test_db.db --postgres-config .buildkite/postgres-config.yaml
+coverage run scripts/synapse_port_db --sqlite-database .ci/test_db.db --postgres-config .ci/postgres-config.yaml
diff --git a/.buildkite/sqlite-config.yaml b/.ci/sqlite-config.yaml
similarity index 80%
rename from .buildkite/sqlite-config.yaml
rename to .ci/sqlite-config.yaml
index d16459cfd..3373743da 100644
--- a/.buildkite/sqlite-config.yaml
+++ b/.ci/sqlite-config.yaml
@@ -3,14 +3,14 @@
 # schema and run background updates on it.
 server_name: "localhost:8800"
 
-signing_key_path: ".buildkite/test.signing.key"
+signing_key_path: ".ci/test.signing.key"
 
 report_stats: false
 
 database:
   name: "sqlite3"
   args:
-    database: ".buildkite/test_db.db"
+    database: ".ci/test_db.db"
 
 # Suppress the key server warning.
 trusted_key_servers: []
diff --git a/.buildkite/test_db.db b/.ci/test_db.db
similarity index 100%
rename from .buildkite/test_db.db
rename to .ci/test_db.db
diff --git a/.buildkite/worker-blacklist b/.ci/worker-blacklist
similarity index 100%
rename from .buildkite/worker-blacklist
rename to .ci/worker-blacklist
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 75c2976a2..8736699ad 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -38,20 +38,15 @@ jobs:
     if: ${{ github.base_ref == 'develop'  || contains(github.base_ref, 'release-') }}
     runs-on: ubuntu-latest
     steps:
-      # Note: This and the script can be simplified once we drop Buildkite. See:
-      #   https://github.com/actions/checkout/issues/266#issuecomment-638346893
-      #   https://github.com/actions/checkout/issues/416
       - uses: actions/checkout@v2
         with:
           ref: ${{ github.event.pull_request.head.sha }}
           fetch-depth: 0
       - uses: actions/setup-python@v2
       - run: pip install tox
-      - name: Patch Buildkite-specific test script
-        run: |
-          sed -i -e 's/\$BUILDKITE_PULL_REQUEST/${{ github.event.number }}/' \
-            scripts-dev/check-newsfragment
       - run: scripts-dev/check-newsfragment
+        env:
+          PULL_REQUEST_NUMBER: ${{ github.event.number }}
 
   lint-sdist:
     runs-on: ubuntu-latest
@@ -144,7 +139,7 @@ jobs:
         uses: docker://ubuntu:bionic # For old python and sqlite
         with:
           workdir: /github/workspace
-          entrypoint: .buildkite/scripts/test_old_deps.sh
+          entrypoint: .ci/scripts/test_old_deps.sh
         env:
           TRIAL_FLAGS: "--jobs=2"
       - name: Dump logs
@@ -197,12 +192,12 @@ jobs:
       volumes:
         - ${{ github.workspace }}:/src
       env:
-        BUILDKITE_BRANCH: ${{ github.head_ref }}
         POSTGRES: ${{ matrix.postgres && 1}}
         MULTI_POSTGRES: ${{ (matrix.postgres == 'multi-postgres') && 1}}
         WORKERS: ${{ matrix.workers && 1 }}
         REDIS: ${{ matrix.redis && 1 }}
         BLACKLIST: ${{ matrix.workers && 'synapse-blacklist-with-workers' }}
+        TOP: ${{ github.workspace }}
 
     strategy:
       fail-fast: false
@@ -232,7 +227,7 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - name: Prepare test blacklist
-        run: cat sytest-blacklist .buildkite/worker-blacklist > synapse-blacklist-with-workers
+        run: cat sytest-blacklist .ci/worker-blacklist > synapse-blacklist-with-workers
       - name: Run SyTest
         run: /bootstrap.sh synapse
         working-directory: /src
@@ -252,6 +247,8 @@ jobs:
     if: ${{ !failure() && !cancelled() }} # Allow previous steps to be skipped, but not fail
     needs: linting-done
     runs-on: ubuntu-latest
+    env:
+      TOP: ${{ github.workspace }}
     strategy:
       matrix:
         include:
@@ -281,13 +278,7 @@ jobs:
       - uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}
-      - name: Patch Buildkite-specific test scripts
-        run: |
-          sed -i -e 's/host="postgres"/host="localhost"/' .buildkite/scripts/postgres_exec.py
-          sed -i -e 's/host: postgres/host: localhost/' .buildkite/postgres-config.yaml
-          sed -i -e 's|/src/||' .buildkite/{sqlite,postgres}-config.yaml
-          sed -i -e 's/\$TOP/\$GITHUB_WORKSPACE/' .coveragerc
-      - run: .buildkite/scripts/test_synapse_port_db.sh
+      - run: .ci/scripts/test_synapse_port_db.sh
 
   complement:
     if: ${{ !failure() && !cancelled() }}
diff --git a/MANIFEST.in b/MANIFEST.in
index 0522319c4..44d5cc761 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -44,9 +44,9 @@ include book.toml
 include pyproject.toml
 recursive-include changelog.d *
 
-prune .buildkite
 prune .circleci
 prune .github
+prune .ci
 prune contrib
 prune debian
 prune demo/etc
diff --git a/changelog.d/10573.misc b/changelog.d/10573.misc
new file mode 100644
index 000000000..fc9b1a2f7
--- /dev/null
+++ b/changelog.d/10573.misc
@@ -0,0 +1 @@
+Remove references to BuildKite in favour of GitHub Actions.
\ No newline at end of file
diff --git a/scripts-dev/check-newsfragment b/scripts-dev/check-newsfragment
index af6d32e33..393a548d5 100755
--- a/scripts-dev/check-newsfragment
+++ b/scripts-dev/check-newsfragment
@@ -11,7 +11,7 @@ set -e
 git remote set-branches --add origin develop
 git fetch -q origin develop
 
-pr="$BUILDKITE_PULL_REQUEST"
+pr="$PULL_REQUEST_NUMBER"
 
 # if there are changes in the debian directory, check that the debian changelog
 # has been updated
diff --git a/scripts-dev/lint.sh b/scripts-dev/lint.sh
index 869eb2372..809eff166 100755
--- a/scripts-dev/lint.sh
+++ b/scripts-dev/lint.sh
@@ -94,7 +94,7 @@ else
           "scripts-dev/build_debian_packages"
           "scripts-dev/sign_json"
           "scripts-dev/update_database"
-          "contrib" "synctl" "setup.py" "synmark" "stubs" ".buildkite"
+          "contrib" "synctl" "setup.py" "synmark" "stubs" ".ci"
       )
   fi
 fi
diff --git a/tox.ini b/tox.ini
index da77d124f..5a62ec76c 100644
--- a/tox.ini
+++ b/tox.ini
@@ -49,7 +49,7 @@ lint_targets =
     contrib
     synctl
     synmark
-    .buildkite
+    .ci
     docker
 
 # default settings for all tox environments