Holt joins the Latics for an undisclosed fee from Norwich City having spent four years at Carrow Road.
The 32-year-old becomes manager Owen Coyle's seventh summer signing for the newly-relegated club, and he believes that Holt will add an extra dimension to his side.
"This is a fantastic piece of business for us at a really good price. Grant is a proven goalscorer at every level," Coyle told reporters.
"He will definitely bring something new to the table that we were missing in the squad."
Holt also expressed his delight at having joined Wigan and thanked Norwich for his time at the club.
"Delighted to announce I have signed for Wigan on three year deal. Start of a new chapter. To all Norwich thank for a fabulous 4 years," he wrote on Twitter.
"Thanks for all your lovely messages been a great four years with the club great memories and some great friends made along the way."
Holt, who scored 78 goals in 168 appearances for the Canaries, was voted as their Player of the Year in 2010, 2011 and 2012.