diff --git a/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js b/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js
--- a/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js
+++ b/keyserver/flow-typed/npm/@commapp/olm_vx.x.x.js
@@ -173,6 +173,7 @@
     PRIVATE_KEY_LENGTH: typeof PRIVATE_KEY_LENGTH,
     Account: typeof Account,
     Utility: typeof Utility,
+    Session: typeof Session,
   };
 
 }
diff --git a/keyserver/src/creators/olm-session-creator.js b/keyserver/src/creators/olm-session-creator.js
new file mode 100644
--- /dev/null
+++ b/keyserver/src/creators/olm-session-creator.js
@@ -0,0 +1,57 @@
+// @flow
+
+import type { Account as OlmAccount } from '@commapp/olm';
+
+import { ServerError } from 'lib/utils/errors.js';
+
+import { dbQuery, SQL } from '../database/database.js';
+import { fetchCallUpdateOlmAccount } from '../updaters/olm-account-updater.js';
+import { createPickledOlmSession } from '../utils/olm-utils.js';
+
+async function createOlmSession(
+  initialEncryptedMessage: string,
+  olmSessionType: 'primary' | 'notifications',
+  cookieID: string,
+): Promise<void> {
+  const isPrimary = olmSessionType === 'primary';
+
+  let account;
+  const accountCallback = async (callbackAccount: OlmAccount) => {
+    account = callbackAccount;
+  };
+  await fetchCallUpdateOlmAccount(olmSessionType, accountCallback);
+  if (!account) {
+    throw new ServerError('missing_olm_account');
+  }
+
+  const [picklingKeyResult] = await dbQuery(
+    SQL`
+      SELECT pickling_key
+      FROM keyserver_olm_accounts 
+      WHERE is_primary = ${isPrimary}
+    `,
+  );
+  if (picklingKeyResult.length === 0) {
+    throw new ServerError('missing_account_pickling_key');
+  }
+  const picklingKey = picklingKeyResult[0].pickling_key;
+
+  const pickledOlmSession = await createPickledOlmSession(
+    account,
+    picklingKey,
+    initialEncryptedMessage,
+  );
+
+  // We match the native client behavior here where olm session is overwritten
+  // in case it is initialized twice for the same pair of identities
+  await dbQuery(
+    SQL`
+      INSERT INTO olm_sessions (cookie_id, is_primary, pickled_olm_session)
+      VALUES (${cookieID}, ${isPrimary}, ${pickledOlmSession})
+      ON DUPLICATE KEY UPDATE
+        pickled_olm_session = ${pickledOlmSession}
+    `,
+  );
+}
+
+export { createOlmSession };
diff --git a/keyserver/src/utils/olm-utils.js b/keyserver/src/utils/olm-utils.js
--- a/keyserver/src/utils/olm-utils.js
+++ b/keyserver/src/utils/olm-utils.js
@@ -4,6 +4,7 @@
 import type {
   Account as OlmAccount,
   Utility as OlmUtility,
+  Session as OlmSession,
 } from '@commapp/olm';
 import uuid from 'uuid';
 
@@ -39,6 +40,27 @@
   return account;
 }
 
+async function createPickledOlmSession(
+  account: OlmAccount,
+  accountPicklingKey: string,
+  initialEncryptedMessage: string,
+): Promise<string> {
+  await olm.init();
+  const session = new olm.Session();
+  session.create_inbound(account, initialEncryptedMessage);
+  return session.pickle(accountPicklingKey);
+}
+
+async function unpicklePickledOlmSession(
+  pickledSession: string,
+  picklingKey: string,
+): Promise<OlmSession> {
+  await olm.init();
+  const session = new olm.Session();
+  session.unpickle(picklingKey, pickledSession);
+  return session;
+}
+
 let cachedOLMUtility: OlmUtility;
 function getOlmUtility(): OlmUtility {
   if (cachedOLMUtility) {
@@ -79,7 +101,9 @@
 
 export {
   createPickledOlmAccount,
+  createPickledOlmSession,
   getOlmUtility,
   unpicklePickledOlmAccount,
+  unpicklePickledOlmSession,
   validateAccountPrekey,
 };
diff --git a/web/flow-typed/npm/@commapp/olm_vx.x.x.js b/web/flow-typed/npm/@commapp/olm_vx.x.x.js
--- a/web/flow-typed/npm/@commapp/olm_vx.x.x.js
+++ b/web/flow-typed/npm/@commapp/olm_vx.x.x.js
@@ -173,6 +173,7 @@
     PRIVATE_KEY_LENGTH: typeof PRIVATE_KEY_LENGTH,
     Account: typeof Account,
     Utility: typeof Utility,
+    Session: typeof Session,
   };
 
 }