The Chicago Cubs selected Harrison in the sixth round of the 2008 MLB draft.He became the first Bearcat drafted in the first ten rounds since Kevin Youkilis was taken in the eighth round of the 2001 draft by the Boston Red Sox. In 2008–09, Harrison made 3 stops in the Cubs’ farm system: Class A- Boise Hawks, Class APeoria Chiefs, and Class A+ Daytona Cubs. His impressive accomplishments at the plate could hardly go unnoticed.
Pittsburgh Pirates
On July 30, 2009, the Cubs traded Harrison, along with Kevin Hart, and José Ascanio to the Pittsburgh Pirates for pitchers John Grabow and Tom Gorzelanny. Harrison had his contract purchased by the Pirates on May 30, 2011. He made his MLB debut on May 31, 2011, and recorded his first MLB hit, off New York Mets pitcher R.A. Dickey. On May 18, 2012, Harrison broke up Justin Verlander's no-hitter in the ninth inning, which would have been the third no-hitter of Verlander's career. Harrison was optioned to the Triple-A Indianapolis Indians on April 14, 2013. He was recalled on May 7 when James McDonald was placed on the disabled list. Harrison was optioned back to Indianapolis on May 8 when Duke Welker was recalled. Harrison was optioned back to Indianapolis on May 31. On July 6, 2014, Harrison was selected to his first career All-Star Game, along with teammates Andrew McCutchen and Tony Watson. At the time of his selection, Harrison was hitting.298 through 72 games. He had played 5 different positions throughout the season, and was listed as a utility player for the All-Star Game. Despite his role as a utility player throughout the 2014 season, Harrison played in 143 games and logged enough at bats to qualify for the National League batting title. Finishing the season with a.315 batting average, he came in second to Justin Morneau of the Colorado Rockies. Morneau won the title with a.319 average after sitting out the team's final two games, one of which lasted twelve innings. Harrison continued to play multiple positions for the Pirates. He spent most of his time at third base following Pedro Álverez's move to 1st Base. Harrison finished 2014 with the best statistics of his career with a.315 batting average, 13 home runs, 52 runs batted in, and finished ninth in voting for NL MVP. Harrison began the 2015 season as the starting third baseman for the Pirates, agreeing to a four-year contract extension through 2018, with club options for 2019 and 2020, shortly after the season's start. Following the 2015 season, the Pirates' regular starting Second baseman, Neil Walker, was traded to the New York Mets. Harrison then became the starting second baseman for the 2016 season. On August 23, 2017, against the Los Angeles Dodgers, Harrison became the first player in MLB history to break up a no-hitter in extra innings with a walk-off home run. The home run was hit in the tenth inning, off of pitcher Rich Hill, to give the Pirates a 1-0 win. On September 3, 2017, Harrison went on the disabled list due to a fracture of the fifth metacarpal on his left hand. On April 15, 2018, Harrison was hit by a pitch on the left hand and left the game. The next day, on April 16, he was ruled out for 6 weeks due to a fracture of the fifth metacarpal, a similar injury he suffered last September. The Pirates declined his 2019 contract option and made him a free agent on October 31, 2018.
Detroit Tigers
On February 23, 2019, Harrison signed a one-year contract with the Detroit Tigers. Upon joining the team, he switched his number to 1 to honor former second baseman Lou Whitaker. Harrison batted.176 in 36 games before he strained a hamstring in May. The Tigers released him on August 9, while he was still rehabilitating from the injury.
On November 26, 2019, Harrison signed a minor league contract with the Philadelphia Phillies. On July 21, 2020, Harrison requested and was granted his release from the Philadelphia Phillies.
Washington Nationals
On July 27, 2020, Harrison signed a one-year major league contract with the Washington Nationals.
Harrison is the nephew of former major league outfielder and coach John Shelby. Harrison's brother, Vince Harrison, played minor league baseball from 2001-2011, before joining the Pirates organization as a player-coach. Beginning in 2014, Harrison started a youth baseball camp for kids and teens in Cincinnati. Harrison's brother Vince also sponsors and helps with the event. Harrison and his wife, Brittney, have two daughters; one born in 2014, and one born in 2017.
