The 27-year-old has signed a three-year deal with the Latics for an undisclosed fee.
Riera scored 13 goals in 37 matches last season, though his form could not stop Osasuna being relegated from La Liga.
"He netted the majority of the goals for Osasuna last season and shone out in a difficult season for the club," Wigan boss Uwe Rosler told the club's official website.
"I think our fans will like him; he is very direct and physical, good in the air, a real worker, but also has an eye for goal, scoring the majority of his goals inside the box.
"He has attracted the attention of many clubs and we are delighted he has agreed to join us."
Wigan get their Championship campaign underway at home to Reading on August 9.