The Scotland international, whose contract with the Welsh club expired this summer, reportedly turned down a number of offers before agreeing a deal with the Latics.
Following the loss of several key first-team players, Wigan manager Uwe Rosler was keen to bring in an experienced midfielder and is convinced Cowie is the man for the job.
"After we lost Jordi Gomez, Jack Collison, Josh McEachran, added to the longer-term injuries we've had with Ben (Watson) and Chris (McCann), I wanted to bring in an energetic player with experience who knows all about getting out of this league," the German boss told the club's official website.
"Don also played over 20 games last season in the Premier League; he's 31 but he's an extremely professional person and I've known about him for quite some time.
"From his training regime to the way he lives and breathes football he has the attributes to allow him to play football until his late 30s.
"I think he knows the position, he has the ability to play a high-pressing game and an attacking forward game and I think he will add experience, reliability, a technical ability where all our players have to be so I look forward to working with him."
Cowie becomes Rosler's fifth summer signing following in the footsteps of Andrew Taylor, Aaron Taylor-Sinclair, James Tavernier and Oriol Riera.