diff --git a/zerver/lib/soft_deactivation.py b/zerver/lib/soft_deactivation.py
new file mode 100644
index 0000000000..b9ff4ac8d4
--- /dev/null
+++ b/zerver/lib/soft_deactivation.py
@@ -0,0 +1,35 @@
+from __future__ import absolute_import
+
+from django.db import transaction
+
+from zerver.models import UserProfile, UserMessage, RealmAuditLog
+
+from django.utils.timezone import now as timezone_now
+
+from typing import List
+
+def do_soft_deactivate_user(user_profile):
+    # type: (UserProfile) -> None
+    user_profile.last_active_message_id = UserMessage.objects.filter(
+        user_profile=user_profile).order_by(
+        '-message__id')[0].message_id
+    user_profile.long_term_idle = True
+    user_profile.save(update_fields=[
+        'long_term_idle',
+        'last_active_message_id'])
+
+def do_soft_deactivate_users(users):
+    # type: (List[UserProfile]) -> None
+    with transaction.atomic():
+        realm_logs = []
+        for user in users:
+            do_soft_deactivate_user(user)
+            event_time = timezone_now()
+            log = RealmAuditLog(
+                realm=user.realm,
+                modified_user=user,
+                event_type='user_soft_deactivated',
+                event_time=event_time
+            )
+            realm_logs.append(log)
+        RealmAuditLog.objects.bulk_create(realm_logs)
diff --git a/zerver/tests/test_soft_deactivation.py b/zerver/tests/test_soft_deactivation.py
new file mode 100644
index 0000000000..38a322b907
--- /dev/null
+++ b/zerver/tests/test_soft_deactivation.py
@@ -0,0 +1,39 @@
+# -*- coding: utf-8 -*-
+from __future__ import absolute_import
+
+from zerver.lib.soft_deactivation import (
+    do_soft_deactivate_user,
+    do_soft_deactivate_users
+)
+
+from zerver.lib.test_classes import (
+    ZulipTestCase,
+)
+
+class UserSoftDeactivationTests(ZulipTestCase):
+
+    def test_do_soft_deactivate_user(self):
+        # type: () -> None
+        user = self.example_user('hamlet')
+        self.assertFalse(user.long_term_idle)
+
+        do_soft_deactivate_user(user)
+
+        user.refresh_from_db()
+        self.assertTrue(user.long_term_idle)
+
+    def test_do_soft_deactivate_users(self):
+        # type: () -> None
+        users = [
+            self.example_user('hamlet'),
+            self.example_user('iago'),
+            self.example_user('cordelia'),
+        ]
+        for user in users:
+            self.assertFalse(user.long_term_idle)
+
+        do_soft_deactivate_users(users)
+
+        for user in users:
+            user.refresh_from_db()
+            self.assertTrue(user.long_term_idle)