Disclosed are various embodiments for intelligent backfill and data migration operations performed using an event processing architecture. A backfill system may identify backfill operations to migrate legacy data from a first system to a second system and generate events to provide to an event processor, where each of the events causes a backfill operation to be performed. Access to the events may be selectively controlled using an event processing queue such that the events are processed and the backfill operations are performed when a computing resource has available computing resources, regardless of a time of day.