The 27-year-old has joined for an undisclosed fee, agreeing a two-and-a-half-year contract with the relegation-threatened Premier League club.
Wigan boss Roberto Martinez told his club's website: "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."
Beausejour joined Birmingham in the summer of 2010 from Mexican side Club America.
He played 56 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 .
Martinez added: "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, who has made 43 appearances for Chile and scored against Honduras in the 2010 World Cup, was impressed by his new manager's ambition.
"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."
While Beausejour's transfer to Wigan has now been confirmed, it seems any move for Bristol City striker Nicky Maynard is still some way off.
The wheels appeared to be very much in motion regarding Maynard's potential move to the DW Stadium when a statement on the City website on Wednesday said the npower Championship outfit had given the Latics permission to speak to the 25-year-old, adding that discussions over a fee were "at an advanced stage".
However, Wigan released a statement of their own on Wednesday, saying: "Contrary to heavy media speculation, no official bid has been made to Bristol City for striker Nicky Maynard and there have been no official talks with the player or the club."
In the statement, Latics chief executive Jonathan Jackson added: "An informal inquiry was made as to the player's availability last week, but that really is as far as it goes at this stage.
"We are therefore disappointed by suggestions that talks are in an advanced stage.
"Some reports even suggest the player has turned [down] a move to Wigan Athletic, when in fact, no bid has been lodged.
"It is normal for clubs to communicate with each other to ascertain the availability of players - especially during a transfer window.
"However, we believe these conversations should remain confidential, otherwise, as we have seen in this instance, it can lead to exaggerated speculation."
Maynard has been made available for transfer by the Robins after ending talks over a possible new contract with the club.
An unused substitute in Saturday's 2-1 win over Doncaster, he has made 130 first-team appearances for the Robins, scoring 46 goals, since arriving from Crewe in a £2.25million deal in July 2008.