He played in 31 regular-season games (four starts) since the trade, totaling 44 catches for 484 yards and three touchdowns. He played in five playoff games, with seven catches for 120 yards and two touchdowns.
The Patriots relied on Dorsett more early in the 2018 season, when Julian Edelman was serving a four-game NFL suspension. Once Edelman returned and receiver Josh Gordon was acquired in a mid-September trade and eased into the team's system, Dorsett's playing time diminished.
Still, he showed a knack for catching most everything thrown in his direction and rising up in critical situations.
Dorsett told ESPN earlier this year that his goal is to be a starter, but he left open a return to New England.
"Me and him have a good relationship," he said of coach Bill Belichick. "I believe he wants me back. I do believe that. At the end of the day, you really never know. I'm going in [to free agency] with blinders. I don't really know what's going to happen.
"Obviously, I want to win. I don't want to play this game just to play it. I play because I love it and the relationships. The whole organization was just amazing. Obviously, everyone has their personal goals, and I do want to be a bigger role. That's just the kind of guy I am. And helping the team win."
Dorsett, who turned 26 in January, entered the NFL as a first-round draft choice (No. 29 overall) of the Colts in 2015. He has 95 receptions for 1,237 yards and six touchdowns in 57 games.
NFL Network first reported the agreement.