Tejada was born in Santiago de Veraguas in western Panama to Rubén, Sr., a mechanic, and Donaji Tejada, a secretary. Tejada also has a younger brother, Ernie. Tejada grew up mere feet away from Omar Torrijos Herrera Stadium where his father was also a pitcher for Los Indios de Veraguas.
Growing up, Tejada's favorite baseball players were shortstops Derek Jeter and Omar Vizquel. In 2001, Tejada played for the Santiago de Veraguas Little League team which represented the Latin American region at the Little League World Series. In 2003, at 13 years old, Tejada began playing for Los Indios de Veraguas’ junior team as a pitcher.
Tejada signed with the Mets as an international free agent in 2006. He debuted in professional baseball in 2007. He has played for the Gulf Coast Mets, Venezuela Mets, St. Lucie Mets and Binghamton Mets. He also played for the Surprise Rafters of the Arizona Fall League.
Tejada was invited to spring training with the Mets in 2010. He was the youngest position player on the Mets Opening Day roster since Tim Foli in 1971. On April 7, 2010 he made his major league debut and went 0-for-2 with a HBP in 3 Plate Appearances. On April 9, 2010 he recorded his first major league hit off the Washington Nationals' Tyler Walker.
On June 4, 2010 the Mets re-called up Tejada to replace Luis Castillo. The Mets won the game to a score of 4–3 against the Florida Marlins at Citi Field.
With the activation of Luis Castillo from the DL on July 19, 2010, the Mets optioned Tejada to the Triple-A Buffalo Bisons. He hit .212 in 104 at-bats with the Mets.
He was re-called on August 7, after Alex Cora was released and Jesús Feliciano was demoted to Triple A Buffalo Bisons.
On September 5, 2010 in the seventh inning Tejada hit his first major league home run off Cubs pitcher Marcos Mateo on the first pitch.
On May 17, 2011 Tejada was called up to play second base, thus moving Justin Turner to third base for the injured David Wright. He ended the season with a .284 batting average in 328 at-bats.
Once Jose Reyes signed with the Miami Marlins, Rubén Tejada became the New York Mets starting shortstop for the 2012 season. On August 1, 2012, Tejada hit his second home run in the majors against Matt Cain of the Giants, his first home run since September 5, 2010.
Tejada was placed on the 15-day disabled list with a strained right quad and called up shortstop Omar Quintanilla from the Mets triple-A affiliate Las Vegas 51s to take his spot on the roster. After Quintanilla's unexpected performance however, the Mets optioned Tejada to Las Vegas.
Tejada suffered a broken right fibula in the second game of the 2015 NLDS vs the Dodgers as a result of Chase Utley sliding into him while ill advisedly turning his back to the play. Utley did not aim for the base but rather right at Tejada to break up a double play "in violation of Official Baseball Rule 5.09 (a) (13), which is designed to protect fielders from precisely this type of rolling block that occurs away from the base." In addition to being kicked in the head during the slide Utley was suspended for two games as a result but later successfully appealed the suspension.
On March 15, 2016, the Mets placed Tejada on waivers, and released him the next day after clearing waviers.
On March 19, 2016, Tejada signed a one-year contract worth $1.5 million with the St. Louis Cardinals. Expected to fill in for the injured Jhonny Peralta at shortstop, Tejada himself injured his quad in the final game before the season, landing on the disabled list to begin the season. Tejada was activated on April 18, but the opening at shortstop was no longer there, having been filled instead by Aledmys Díaz. Tejada made his first major league appearance as a pitcher on May 20 in the ninth inning at Busch Stadium against the Arizona Diamondbacks, pitching one complete inning while allowing two earned runs, on back-to-back home runs to Chris Herrmann and Brandon Drury. The Cardinals designated Tejada for assignment on May 28. He had six hits in 34 at bats. Tejada declined the outright assignment, becoming a free agent.
On June 13, Tejada signed a minor league contract with the San Francisco Giants. On June 29, Tejada was called up and started at third base after Matt Duffy was put on the 15-day disabled list. On July 20, he was designated for assignment by San Francisco to make room for Matt Cain who was returning from the disabled list.
On December 12, 2016, Tejada signed a minor league contract with the New York Yankees.
Tejada played for Panama's national baseball team during the 2009 World Baseball Classic and the 2013 World Baseball Classic qualifying tournament.