diff --git a/changelog.d/18418.removal b/changelog.d/18418.removal
new file mode 100644
index 00000000000..ff1d081d8fe
--- /dev/null
+++ b/changelog.d/18418.removal
@@ -0,0 +1 @@
+Stop adding the "origin" field to newly-created events (PDUs).
\ No newline at end of file
diff --git a/contrib/graph/graph.py b/contrib/graph/graph.py
index 1d74fee822c..a16c6fd2878 100644
--- a/contrib/graph/graph.py
+++ b/contrib/graph/graph.py
@@ -45,6 +45,8 @@ def make_graph(pdus: List[dict], filename_prefix: str) -> None:
     colors = {"red", "green", "blue", "yellow", "purple"}
 
     for pdu in pdus:
+        # TODO: The "origin" field have since been removed from events generated
+        # by Synapse.
         origins.add(pdu.get("origin"))
 
     color_map = {color: color for color in colors if color in origins}
diff --git a/docs/admin_api/event_reports.md b/docs/admin_api/event_reports.md
index 9075e928822..225b4317155 100644
--- a/docs/admin_api/event_reports.md
+++ b/docs/admin_api/event_reports.md
@@ -117,7 +117,6 @@ It returns a JSON body like the following:
         "hashes": {
             "sha256": "xK1//xnmvHJIOvbgXlkI8eEqdvoMmihVDJ9J4SNlsAw"
         },
-        "origin": "matrix.org",
         "origin_server_ts": 1592291711430,
         "prev_events": [
             "$YK4arsKKcc0LRoe700pS8DSjOvUT4NDv0HfInlMFw2M"
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index a85e66d6bf7..c77d569e2e7 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -208,7 +208,6 @@ def __init__(
     depth: DictProperty[int] = DictProperty("depth")
     content: DictProperty[JsonDict] = DictProperty("content")
     hashes: DictProperty[Dict[str, str]] = DictProperty("hashes")
-    origin: DictProperty[str] = DictProperty("origin")
     origin_server_ts: DictProperty[int] = DictProperty("origin_server_ts")
     room_id: DictProperty[str] = DictProperty("room_id")
     sender: DictProperty[str] = DictProperty("sender")
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index 76df083d691..8b776a2097a 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -319,7 +319,6 @@ def create_local_event_from_event_dict(
     if format_version == EventFormatVersions.ROOM_V1_V2:
         event_dict["event_id"] = _create_event_id(clock, hostname)
 
-    event_dict["origin"] = hostname
     event_dict.setdefault("origin_server_ts", time_now)
 
     event_dict.setdefault("unsigned", {})
diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index d1fb026cd63..15095cc4ef9 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -67,7 +67,6 @@ def validate_new(self, event: EventBase, config: HomeServerConfig) -> None:
             "auth_events",
             "content",
             "hashes",
-            "origin",
             "prev_events",
             "sender",
             "type",
@@ -77,13 +76,6 @@ def validate_new(self, event: EventBase, config: HomeServerConfig) -> None:
             if k not in event:
                 raise SynapseError(400, "Event does not have key %s" % (k,))
 
-        # Check that the following keys have string values
-        event_strings = ["origin"]
-
-        for s in event_strings:
-            if not isinstance(getattr(event, s), str):
-                raise SynapseError(400, "'%s' not a string type" % (s,))
-
         # Depending on the room version, ensure the data is spec compliant JSON.
         if event.room_version.strict_canonicaljson:
             validate_canonicaljson(event.get_pdu_json())
diff --git a/synapse/util/caches/__init__.py b/synapse/util/caches/__init__.py
index df8829baeba..76e6e139c6f 100644
--- a/synapse/util/caches/__init__.py
+++ b/synapse/util/caches/__init__.py
@@ -225,7 +225,7 @@ def register_cache(
         "depth",
         "event_id",
         "hashes",
-        "origin",
+        "origin",  # old events were created with an origin field.
         "origin_server_ts",
         "prev_events",
         "room_id",
diff --git a/tests/crypto/test_event_signing.py b/tests/crypto/test_event_signing.py
index d7b9fb8bc6f..175b2aa0d02 100644
--- a/tests/crypto/test_event_signing.py
+++ b/tests/crypto/test_event_signing.py
@@ -48,7 +48,6 @@ def setUp(self) -> None:
     def test_sign_minimal(self) -> None:
         event_dict = {
             "event_id": "$0:domain",
-            "origin": "domain",
             "origin_server_ts": 1000000,
             "signatures": {},
             "type": "X",
@@ -80,7 +79,6 @@ def test_sign_message(self) -> None:
         event_dict = {
             "content": {"body": "Here is the message content"},
             "event_id": "$0:domain",
-            "origin": "domain",
             "origin_server_ts": 1000000,
             "type": "m.room.message",
             "room_id": "!r:domain",
diff --git a/tests/events/test_utils.py b/tests/events/test_utils.py
index 654e6521a20..6f8a36d7d42 100644
--- a/tests/events/test_utils.py
+++ b/tests/events/test_utils.py
@@ -122,7 +122,6 @@ def test_basic_keys(self) -> None:
                 "prev_events": "prev_events",
                 "prev_state": "prev_state",
                 "auth_events": "auth_events",
-                "origin": "domain",
                 "origin_server_ts": 1234,
                 "membership": "join",
                 # Also include a key that should be removed.
@@ -139,7 +138,6 @@ def test_basic_keys(self) -> None:
                 "prev_events": "prev_events",
                 "prev_state": "prev_state",
                 "auth_events": "auth_events",
-                "origin": "domain",
                 "origin_server_ts": 1234,
                 "membership": "join",
                 "content": {},
@@ -148,13 +146,12 @@ def test_basic_keys(self) -> None:
             },
         )
 
-        # As of room versions we now redact the membership, prev_states, and origin keys.
+        # As of room versions we now redact the membership and prev_states keys.
         self.run_test(
             {
                 "type": "A",
                 "prev_state": "prev_state",
                 "membership": "join",
-                "origin": "example.com",
             },
             {"type": "A", "content": {}, "signatures": {}, "unsigned": {}},
             room_version=RoomVersions.V11,
@@ -238,7 +235,6 @@ def test_create(self) -> None:
             {
                 "type": "m.room.create",
                 "content": {"not_a_real_key": True},
-                "origin": "some_homeserver",
                 "nonsense_field": "some_random_garbage",
             },
             {
diff --git a/tests/federation/test_federation_server.py b/tests/federation/test_federation_server.py
index 42dc8447349..439fecbd61f 100644
--- a/tests/federation/test_federation_server.py
+++ b/tests/federation/test_federation_server.py
@@ -533,7 +533,6 @@ def test_strip_unauthorized_unsigned_values(self) -> None:
             "depth": 1000,
             "origin_server_ts": 1,
             "type": "m.room.member",
-            "origin": "test.servx",
             "content": {"membership": "join"},
             "auth_events": [],
             "unsigned": {"malicious garbage": "hackz", "more warez": "more hackz"},
@@ -550,7 +549,6 @@ def test_strip_event_maintains_allowed_fields(self) -> None:
             "depth": 1000,
             "origin_server_ts": 1,
             "type": "m.room.member",
-            "origin": "test.servx",
             "auth_events": [],
             "content": {"membership": "join"},
             "unsigned": {
@@ -577,7 +575,6 @@ def test_strip_event_removes_fields_based_on_event_type(self) -> None:
             "depth": 1000,
             "origin_server_ts": 1,
             "type": "m.room.power_levels",
-            "origin": "test.servx",
             "content": {},
             "auth_events": [],
             "unsigned": {