Bearman spent five years at Rodney Parade but has now opted to join the reigning Magners League Champions until the end of the 2012/13 campaign.
"This is an excellent opportunity for me to play top level rugby that I couldn't turn down," said Bearman.
"I've enjoyed five good years at the Dragons but I felt that the time was right for a new challenge and a change of environment.
"There were four or five really good offers on the table but it was the Ospreys who really impressed me.
"The management at the Ospreys have a clear plan for what they want to achieve, and I really like what I've seen of the young talent that has been playing over the last couple of months.
"I've got a lot of experience that I can bring to this young squad, I've played a lot of rugby and I hope I'll be able to give that something extra to the group, including my ball carrying ability, something all teams need.
"I've had a look around at the excellent training facilities, spoken to the coaches, and with me being settled in Wales with my girlfriend this move is the obvious one for me. I can't wait to get my teeth into a new challenge."
Bearman has twice come close to winning a Welsh cap, with a groin injury ruling him out of contention for both the 2009 Autumn Internationals and the 2010 RBS 6 Nations.
The same injury has also had an impact on the 32-year-old's regional appearances this season, with Bearman playing the opening Magners League match at Connacht in early September before spending the nxt five months on the sidelines.
However, the former Cornish Pirates blindside cum No8, who qualifies for Wales on residency grounds, has since started each of the Dragons' seven most recent fixtures, playing the full 80 minutes in six of those games.
The Ospreys hope Bearman's experience will help them push forward on the domestic and European front, starting at a time when they could well be missing more than a dozen Wales stars for the 2011 World Cup.
"With his experience, I've no doubt that he will prove to be a huge asset to the Ospreys environment, on and off the field," said the Ospreys' elite performance director Andrew Hore.
"Joe comes to us with an excellent reputation for being an honest, hard working individual, who thrives on the physical side of the game and is particularly renowned for his ability to make the hard yards with ball in hand.
"His signing is not just about what he brings to the team as a player, it is part of a bigger all round plan, to assist in the development of our younger players coming through. Joe leads by example, and displays all the characteristics that we want from our up and coming age-grade players."