Blanco signed with the Atlanta Braves on July 4, 2008, as an undrafted free agent. He beat out Josh Anderson in spring training to become the Braves backup outfielder in 2008. He began to see regular playing time after Mark Kotsay injured his back on May 26. In 2008, he had the lowest home run per plate appearance percentage in the majors .
On May 8, 2011, Blanco was traded to the Washington Nationals in exchange for a player to be named later. During the offseason of 2011, Gregor played in the Venezuelan Winter league and was named the MVP for the 2011 season.
San Francisco Giants
Blanco signed a minor league contract with the San Francisco Giants on November 16, 2011, and was selected to be part of the Giants' 2012 Opening Day roster as an outfielder. On June 13, 2012, Blanco made a fully extended diving catch in deep right-center field, catching the ball in the end of his mitt, to rob Jordan Schafer of a hit in the top of the 7th inning of Matt Cain's perfect game. The Mercury News wrote "In a town very familiar with the words "The Catch", Blanco made one for the ages: he took off on a dead sprint at the crack of the bat and made a diving catch on the warning track in center field, 400 feet from home plate." On July 13, 2013, in a 9-0 win over the San Diego Padres at Petco Park, Blanco caught the final out of Tim Lincecum's first career no-hitter in the ninth inning. It was the first no-hitter in the history of the ballpark. On September 5, 2014, Blanco made an error that ended his 306-game errorless streak. He dropped the ball on a Bryan Holaday line drive. On July 8, 2016, Blanco hit his first career pinch-hit home run, and his first of the season. In 2016 with the Giants he batted.224/.309/.311.
Arizona Diamondbacks
On January 17, 2017, Blanco signed a minor league contract with the Arizona Diamondbacks that included an invitation to spring training. He was released on March 27, and re-signed to a new minor league contract the next day.
San Francisco Giants (second stint)
On January 29, 2018, Blanco signed a minor league contract to return to the Giants. His contract was purchased by the Giants on March 28, 2018, and he was assigned to the Opening Day roster. He was designated for assignment on June 2, 2018. In his second stint, he hit.217/.262/.317 with 2 home runs.
On December 21, 2018, Blanco signed a minor league contract with the New York Mets that included an invitation to spring training. He became a free agent following the 2019 season.
Retirement
On February 6, 2020, Blanco retired to take on a new post in the baseball operations department for MLB.
Personal life
Blanco has three children and a wife named Mirna Blanco. He has a twin brother named Gregory and a younger brother named Gregsman.
