diff --git a/.github/workflows/debs.yml b/.github/workflows/debs.yml
new file mode 100644
index 000000000000..e03a41942695
--- /dev/null
+++ b/.github/workflows/debs.yml
@@ -0,0 +1,44 @@
+# GitHub actions workflow which builds the debian packages.
+
+name: Debs
+
+on:
+  push:
+    branches: ["develop", "release-*"]
+
+permissions:
+  contents: read
+
+jobs:
+  # first get the list of distros to build for.
+  get-distros:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - id: set-distros
+        run: |
+          echo "::set-output name=distros::$(scripts-dev/build_debian_packages --show-dists-json)"
+    # map the step outputs to job outputs
+    outputs:
+      distros: ${{ steps.set-distros.outputs.distros }}
+
+  # now build the packages with a matrix build.
+  build-debs:
+    needs: get-distros
+    name: "Build .deb packages"
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        distro: ${{ fromJson(needs.get-distros.outputs.distros) }}
+
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          path: src
+      - uses: actions/setup-python@v2
+      - run: ./src/scripts-dev/build_debian_packages "${{ matrix.distro }}"
+      - uses: actions/upload-artifact@v2
+        with:
+          name: packages
+          path: debs/*
diff --git a/changelog.d/10248.misc b/changelog.d/10248.misc
new file mode 100644
index 000000000000..5824907bca63
--- /dev/null
+++ b/changelog.d/10248.misc
@@ -0,0 +1 @@
+Build the Debian packages in CI.
diff --git a/scripts-dev/build_debian_packages b/scripts-dev/build_debian_packages
index 546724f89fea..e34e12257ed9 100755
--- a/scripts-dev/build_debian_packages
+++ b/scripts-dev/build_debian_packages
@@ -10,6 +10,7 @@
 # can be passed on the commandline for debugging.
 
 import argparse
+import json
 import os
 import signal
 import subprocess
@@ -34,6 +35,7 @@ By default, builds for all known distributions, but a list of distributions
 can be passed on the commandline for debugging.
 """
 
+projdir = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
 
 class Builder(object):
     def __init__(self, redirect_stdout=False):
@@ -57,9 +59,6 @@ class Builder(object):
             raise
 
     def _inner_build(self, dist, skip_tests=False):
-        projdir = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
-        os.chdir(projdir)
-
         tag = dist.split(":", 1)[1]
 
         # Make the dir where the debs will live.
@@ -93,6 +92,7 @@ class Builder(object):
             ],
             stdout=stdout,
             stderr=subprocess.STDOUT,
+            cwd=projdir,
         )
 
         container_name = "synapse_build_" + tag
@@ -179,6 +179,11 @@ if __name__ == "__main__":
         action="store_true",
         help="skip running tests after building",
     )
+    parser.add_argument(
+        "--show-dists-json",
+        action="store_true",
+        help="instead of building the packages, just list the dists to build for, as a json array",
+    )
     parser.add_argument(
         "dist",
         nargs="*",
@@ -186,4 +191,8 @@ if __name__ == "__main__":
         help="a list of distributions to build for. Default: %(default)s",
     )
     args = parser.parse_args()
-    run_builds(dists=args.dist, jobs=args.jobs, skip_tests=args.no_check)
+    if args.show_dists_json:
+        json.dump(DISTS, sys.stdout)
+        print()
+    else:
+        run_builds(dists=args.dist, jobs=args.jobs, skip_tests=args.no_check)