He played in Major League Baseball (MLB) for the Toronto Blue Jays, Chicago White Sox, Texas Rangers, and Kansas City Royals.

In 2003, he hit .352 with 11 home runs and 82 RBI en route to winning the Double-A Eastern League Most Valuable Player award.

[3] After his participation with the Puerto Rican team in the World Baseball Classic, Ríos began to show why the Blue Jays valued him so highly in his break-out 2006 season.

On June 27 against the Washington Nationals, Ríos fouled a ball off his foot, which resulted in a staph infection and a hospitalization.

[6] In recognition of his outstanding third season in the majors, the young outfielder was rewarded with a spot as a reserve on the American League All-Star Team.

On February 2, 2007, the Blue Jays and Ríos agreed to a one-year, $2.535 million contract to avoid salary arbitration.

[7] Ríos' performance earned him a spot as a reserve on the American League All-Star team[8] and he also agreed to participate in the 2007 State Farm Home Run Derby.

He led the team in all offensive categories during the first half of the season but slumped after the All-Star Break, with his hitting average settling to slightly below .300, and was overtaken by teammate Frank Thomas as HR and RBI leader .

Later that day, Ríos was videotaped cursing a heckling fan after he walked past a child seeking an autograph while leaving a fundraising gala for the Jays Care Foundation.

[3] After a disappointing 2011 season in which he batted a career-low .227, Ríos rebounded to have one of his finest years in 2012, setting career highs with a .304 average, 25 home runs and 91 RBIs.

[21] In his Royals debut on April 6, 2015, Ríos hit a three-run home run in a 10–1 win to cap off a three-hit game.

Although Rios slumped for most of the tournament, he hit a clutch two-run home run against Japan in the semifinals and handed Puerto Rico its first WBC Finals appearance.