Admin Permissions Required
Usually, new custom fields in Salesforce sync over to Marketo automatically. If not, the fields may not be visible to the Marketo Sync user. Here's how you can fix this.
1. Click your name and then select Setup.
2. Enter profile in the left search bar and click Profiles under Manage Users.
3. Click the sync user's profile.
4. Under the Field-Level Security section, click View next to the object that contains the field.
5. Click Edit.
6. Check the Visible checkbox for the field you want to add to the sync and click Save.
Sweet! On the next sync cycle, Marketo will see the field and start the magic.
If the field already has values in Salesforce, those values don't sync over to Marketo until the next record update.