Terms of the deal with the company based in Orlando, Fla., were not disclosed. ESPN.com first reported the agreement.
Company president Marty Graham said the agreement wasn't about the past, but focused on the future. He said the firm has done its research and strongly believes in Braun as an athlete.
A five-time All-Star and the 2011 NL MVP, Braun accepted a 65-game penalty last July for his involvement with Biogenesis, a Florida clinic accused of distributing performance-enhancing drugs. Nike Inc., ended its relationship with Braun afterward.
Braun has apologized several times and returned to the team in spring training.
Graham described 3n2 as a "very niche focused brand" that sells only baseball and softball uniforms and accessories for everyone from Little Leaguers to major leaguers.
Graham said Braun would help them sell their products to serious athletes.
"We think as a young brand that's trying to gain traction in our baseball brand, we think it's a good opportunity," Graham said in a phone interview. "I think he's going to go out and prove that's the case."
In a statement provided by the company, Braun said he was excited about the partnership. He will wear the company's footwear and apparel this season.
Braun, who is also moving from left to right field this year, was batting .636 with two home runs entering Wednesday.
"Certainly it bodes well. I know he's healthy," Graham said. "I think he's had a big chip on his shoulder (to show) that he has some God-given ability."
The company also lists Phillies pitcher A.J. Burnett and Dodgers reliever Chris Perez among other big league endorsers.