Wigan boss Coyle delighted with capture for Norwich's Barnett
Barnett, 27, helped the Canaries win promotion to the Premier League two seasons ago and last term played a part in Cardiff's elevation to the top flight.
Coyle said: "As Manager, to see the desire Leon has to play for Wigan Athletic is tremendous and we're all delighted to have enticed a player of his calibre to our club.
"He has shown his qualities in the Premier League on numerous occasions and has the experience of being successful in a division as tough as the Championship, winning promotion on three separate occasions.
"That kind of experience for someone who is still only 27 years old is fantastic, and I believe that whilst he has much maturity in his play he also has huge potential to become an even better player here at Wigan Athletic."