The 27-year-old signed a two-and-a-half-year contract with Wigan after having underwent a medical earlier on Wednesday.
Beausejour has joined Wigan for an undisclosed fee.
"Jean is a player we have been tracking for a long time since he made a huge impression on us with his role for Chile in the World Cup," Wigan boss Roberto Martinez told the club's official website.
"Now Jean has 18 months of experience in the British game and his dynamism, technical ability and tactical concepts will bring a different dimension into our squad.
"He is ready to bring his own experience and his energy into the fantastic challenge that as a football club we're facing in the next 16 games of the season."
Beausejour said: "Roberto told me about the plans he has for the club and I am really excited to join and meet my team-mates.
"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."