He played for the Chicago White Sox, Seattle Mariners, San Diego Padres, Los Angeles Dodgers, New York Mets, Philadelphia Phillies, and Cincinnati Reds of Major League Baseball, the Kia Tigers of the KBO League, and the Tokyo Yakult Swallows of Nippon Professional Baseball from 2004 to 2012.

On June 17, 2004, while hitting .319 for Albuquerque, he was traded by the Marlins with cash to the Chicago White Sox in exchange for reliever Billy Koch.

After the 2005 season, he was released by the Padres and signed to a minor league contract by the Kansas City Royals, who promptly traded him to the Los Angeles Dodgers during spring training.

On November 25, 2009, Valdez signed a minor league contract with the Philadelphia Phillies and was optioned to the Triple-A Lehigh Valley IronPigs.

The Phillies selected his contract from the minors on April 14, 2010, as a reserve infielder, when Jimmy Rollins went on the disabled list.

In addition to playing shortstop, Valdez filled in at second base for Chase Utley while he was on the disabled list with a hand injury.

On July 29, in a game against the Arizona Diamondbacks, Valdez hit a one-out, walk-off single to score Cody Ransom from second base and give the Phillies a 3-2 win.

Valdez thus became the first position player to earn a win since catcher Brent Mayne won a game for the Colorado Rockies in 2000, and just the second since 1968.

[2][3] According to Elias Sports Bureau, Valdez was the first player to start a game in the field and end up as the winning pitcher since Babe Ruth did so on October 1, 1921.