Martínez began in the Washington Nationals organization, commencing his professional career in 2006. That year, he played for the Vermont Lake Monsters, Savannah Sand Gnats and Potomac Nationals, hitting a combined .265 with 11 stolen bases in 82 games. In 2007, he played for the Hagerstown Suns and hit .250 with 13 stolen bases in 116 games. He played for the Potomac Nationals and Harrisburg Senators in 2009, posting a .259 batting average with 10 steals. In 2010, he played for the Senators and Syracuse Chiefs, hitting a combined .272 with 11 home runs and 23 stolen bases.

Martínez went to San Lorenzo High School and did not attend college. He was never drafted and originally wore number 19 when debuting with the Phillies in 2011.

Martínez began 2013 at Triple-A, but his contract was purchased on May 24 because Chase Utley was placed on the 15-day DL. He was designated for assignment on June 22, and outrighted off the roster on October 3. He elected free agency on October 8. In 29 games for the Phillies in 2013, he hit .175 with 3 RBI.

On December 18, 2013, the Pittsburgh Pirates signed Martínez to a minor league deal. His contract was selected from the Triple-A Indianapolis Indians on June 12, and he was optioned back to Indianapolis on August 19. He was designated for assignment on September 2, 2014, when the contract of Chase d’Arnaud was selected and was added to the 40-man roster. Martínez elected free agency in October 2014.

Martínez signed a minor league deal with the Cleveland Indians on February 11, 2015. On April 9, 2015 he was assigned to the Triple-A Columbus Clippers. The Indians purchased his contract from Columbus on September 4, 2015 and added him to the major-league roster. On July 2, 2016, Martínez was designated for assignment to make room on the 25-man roster for Shawn Morimando after a 19-inning game the day before that exhausted the entire bullpen. He hit .283 in 60 at-bats for the Indians.

On July 8, 2016, Martínez was traded to the Boston Red Sox in exchange for cash. During his time with Boston, Martínez hit .167/.286/.167 with no home runs and no RBI in 6 at bats. Martínez appeared in 4 games and starting in one game, playing in right field.

After being designated for assignment by the Red Sox on August 2, 2016, Martínez was claimed by the Indians off waivers on August 4. Martínez hit into the final out to Kris Bryant in the Indians’ Game 7 loss in the 2016 World Series to the Chicago Cubs, which was their first World Series championship in 108 years. On November 23, 2016, he was outrighted to Triple-A. He signed a new minor league contract with the Indians organization on December 1.

The Indians purchased Martínez’s contract on April 2, 2017, adding him to their 2017 opening day roster. Martínez was designated for assignment on May 14, 2017.

On May 18, 2017, the Tampa Bay Rays acquired Martínez in exchange for cash considerations. He was designated for assignment on June 19 to create room for Trevor Plouffe. He became a free agent on June 23, 2017.

Martínez signed a minor league contract with the Cleveland Indians on June 25, 2017. He elected free agency on November 6, 2017, and signed a minor league contract with the Indians on December 2 with an invitation to spring training in 2018. He elected free agency on November 3, 2018.

On March 11, 2019, Martínez signed with the Lancaster Barnstormers of the independent Atlantic League of Professional Baseball. He re-signed with the team for the 2020 season.