"Although my football journey will take place elsewhere, I appreciate everything that we have achieved and am grateful for our incredible TEAM accomplishments," he wrote.
The 42-year-old Brady is being pursued by multiple teams. Among those known to have met with Brady are the Tampa Bay Buccaneers and Miami Dolphins, but several other franchises were connected to Brady during the offseason.
He won six Super Bowl rings with the Patriots and is a three-time NFL MVP.
Brady negotiated a restructured contract for the 2019 season which stipulated he could not be designated a franchise player and would be a free agent.
Brady played 20 seasons in New England and 13 times the Patriots posted at least 12 victories. Reports on Tuesday suggest the quarterback will join the Tampa Bay Bucaneers.