The 29-year-old missed the Seahawks' Super Bowl triumph as he was suspended by the NFL for breaking their policy on substance abuse, and will miss the first four games of the 2014 season with the Pats.
Browner told reporters: "I want to keep that behind me and move on forward from that situation. Like I said before, I just want to contribute to the Pats and leave that in the past. What I can say is that for the last few months, my future has been in a dark place.
"I made a few mistakes and that's one of the mistakes I regret. I look forward to righting my wrongs and I'm blessed at the opportunity to come play in New England and start on a good foot, so to say."
Browner recorded 19 tackles and one interception for the Seahawks in the 2013 season.