The 27-year-old winger has joined the Latics on a two-and-a-half-year contract for an undisclosed fee.
"Roberto told me about the plans he has for the club and I am really excited to join and meet my team-mates," he said.
"We have a really tough end of the season, but I am really looking forward to the challenge ahead.
"I want to thank all the supporters at Birmingham and now I have to concentrate on getting in the team and doing my best for Wigan Athletic."
Beausejour joined Blues in the summer of 2010 from Mexican side Club America.
He played 39 times for Blues, including last year's Carling Cup final victory over Arsenal and the subsequent Europa League campaign, in which he scored against Club Brugge.