diff --git a/roles/matrix-synapse/defaults/main.yml b/roles/matrix-synapse/defaults/main.yml
index d966665f..c7f0a9f7 100644
--- a/roles/matrix-synapse/defaults/main.yml
+++ b/roles/matrix-synapse/defaults/main.yml
@@ -505,6 +505,27 @@ matrix_synapse_ext_spam_checker_synapse_simple_antispam_git_repository_url: "htt
 matrix_synapse_ext_spam_checker_synapse_simple_antispam_git_version: "923ca5c85b08f157181721abbae50dd89c31e4b5"
 matrix_synapse_ext_spam_checker_synapse_simple_antispam_config_blocked_homeservers: []
 
+# Enable this to activate the Mjolnir Antispam spam-checker module.
+# See: https://github.com/matrix-org/mjolnir#synapse-module
+matrix_synapse_ext_spam_checker_mjolnir_antispam_enabled: false
+matrix_synapse_ext_spam_checker_mjolnir_antispam_git_repository_url: "https://github.com/matrix-org/mjolnir"
+matrix_synapse_ext_spam_checker_mjolnir_antispam_git_version: "70f353fbbad0af469b1001080dea194d512b2815"
+matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_invites: true
+# Flag messages sent by servers/users in the ban lists as spam. Currently
+# this means that spammy messages will appear as empty to users. Default
+# false.
+matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_messages: false
+# Remove users from the user directory search by filtering matrix IDs and
+# display names by the entries in the user ban list. Default false.
+matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_usernames: false
+# The room IDs of the ban lists to honour. Unlike other parts of Mjolnir,
+# this list cannot be room aliases or permalinks. This server is expected
+# to already be joined to the room - Mjolnir will not automatically join
+# these rooms.
+# ["!roomid:example.org"]
+matrix_synapse_ext_spam_checker_mjolnir_antispam_config_ban_lists: []
+
+
 matrix_s3_media_store_enabled: false
 matrix_s3_media_store_custom_endpoint_enabled: false
 matrix_s3_goofys_docker_image: "ewoutp/goofys:latest"
diff --git a/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup.yml b/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup.yml
new file mode 100644
index 00000000..6c45f469
--- /dev/null
+++ b/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup.yml
@@ -0,0 +1,7 @@
+---
+
+- import_tasks: "{{ role_path }}/tasks/ext/mjolnir-antispam/setup_install.yml"
+  when: matrix_synapse_ext_spam_checker_mjolnir_antispam_enabled|bool
+
+- import_tasks: "{{ role_path }}/tasks/ext/mjolnir-antispam/setup_uninstall.yml"
+  when: "not matrix_synapse_ext_spam_checker_mjolnir_antispam_enabled|bool"
diff --git a/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup_install.yml b/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup_install.yml
new file mode 100644
index 00000000..a416e42b
--- /dev/null
+++ b/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup_install.yml
@@ -0,0 +1,52 @@
+---
+
+- name: Ensure git installed (RedHat)
+  yum:
+    name:
+      - git
+    state: present
+    update_cache: no
+  when: "ansible_os_family == 'RedHat'"
+
+- name: Ensure git installed (Debian)
+  apt:
+    name:
+      - git
+    state: present
+    update_cache: no
+  when: "ansible_os_family == 'Debian'"
+
+- name: Ensure git installed (Archlinux)
+  pacman:
+    name:
+      - git
+    state: present
+    update_cache: no
+  when: "ansible_distribution == 'Archlinux'"
+
+- name: Clone mjolnir-antispam git repository
+  git:
+    repo: "{{ matrix_synapse_ext_spam_checker_mjolnir_antispam_git_repository_url }}"
+    version: "{{ matrix_synapse_ext_spam_checker_mjolnir_antispam_git_version }}"
+    dest: "{{ matrix_synapse_ext_path }}/mjolnir"
+  become: true
+  become_user: "{{ matrix_user_username }}"
+
+- set_fact:
+    matrix_synapse_spam_checker: >
+      {{ matrix_synapse_spam_checker }}
+      +
+      [{
+        "module": "mjolnir.AntiSpam",
+        "config": {
+          "block_invites": {{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_invites }},
+          "block_messages": {{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_messages }},
+          "block_usernames": {{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_block_usernames }},
+          "ban_lists": {{ matrix_synapse_ext_spam_checker_mjolnir_antispam_config_ban_lists }}
+        }
+      }]
+
+    matrix_synapse_container_extra_arguments: >
+      {{ matrix_synapse_container_extra_arguments|default([]) }}
+      +
+      ["--mount type=bind,src={{ matrix_synapse_ext_path }}/mjolnir/synapse_antispam/mjolnir,dst={{ matrix_synapse_in_container_python_packages_path }}/mjolnir,ro"]
diff --git a/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup_uninstall.yml b/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup_uninstall.yml
new file mode 100644
index 00000000..d3c52e5f
--- /dev/null
+++ b/roles/matrix-synapse/tasks/ext/mjolnir-antispam/setup_uninstall.yml
@@ -0,0 +1,6 @@
+---
+
+- name: Ensure mjolnir-antispam doesn't exist
+  file:
+    path: "{{ matrix_synapse_ext_path }}/mjolnir-antispam"
+    state: absent
diff --git a/roles/matrix-synapse/tasks/ext/setup.yml b/roles/matrix-synapse/tasks/ext/setup.yml
index 5e06ea9d..31637fa9 100644
--- a/roles/matrix-synapse/tasks/ext/setup.yml
+++ b/roles/matrix-synapse/tasks/ext/setup.yml
@@ -7,3 +7,5 @@
 - import_tasks: "{{ role_path }}/tasks/ext/ldap-auth/setup.yml"
 
 - import_tasks: "{{ role_path }}/tasks/ext/synapse-simple-antispam/setup.yml"
+
+- import_tasks: "{{ role_path }}/tasks/ext/mjolnir-antispam/setup.yml"