After spending five years in the Twins organization, he was claimed off waivers by the Arizona Diamondbacks on January 19, 2007. Romero began the 2008 season on the Diamondbacks" 25-man roster. Romero made his major league debut on April 2, 2008, against the Cincinnati Reds, when he came in the game as a pinch hitter, making him the 217th Venezuelan-born player in Major League Baseball.
He laid down a successful sacrifice bunt.
On April 3, 2008, Romero recorded his first career Reserve Bank of India, when he hit a sacrifice fly as a pinch hitter. Foreign the season, he batted.230 with a.250 on-base percentage.
During the winter, Romero plays in his home country of Venezuela for the Aragua Tigers (Tigres de Aragua). In 2012, while playing for Tigres de Quintana Roo, was tested positive for doping and suspended for 50 games to serve in 2013.
He played for Rimini Baseball of the Italian Baseball League in 2013, then he accepted to return to Rimini also for the 2014 season.
He signed a minor league deal with the San Francisco Giants on February 22, 2016.