The Browns also sent their seventh-round pick to New England and will receive the Patriots' sixth-round pick.
The Browns originally had announced they were releasing McCourty, but they worked out a trade before the release became official at 4 p.m.
Devin McCourty is a Patriots captain, entering his ninth season with the team. He has long expressed a desire to play with his brother.
Jason spent one season with the Browns after playing eight with Tennessee. McCourty played well in 14 starts, with three interceptions, one returned for a touchdown. But he had to suffer through a winless season and voiced some unhappiness late in the season that coach Hue Jackson had said the team did not have the talent to win.
McCourty has one year remaining on his contract and will earn a base salary of $2.375 million. He is due a $375,000 roster bonus on Friday, which will be the Patriots' responsibility. He can earn an additional $250,000 in per-game roster bonuses.
Browns general manager John Dorsey said the team decided to part ways with McCourty because they did not believe he would make the roster. The team signed two defensive backs in free agency -- T.J. Carrie and Terrance Mitchell -- and traded with Green Bay for safety Damarious Randall.
In nine NFL seasons, McCourty has 13 interceptions. At 30, he has the ability to play safety or corner.
ESPN's Mike Reiss contributed to this report.