In the 2012 MLB draft, the San Francisco Giants selected Williamson in the third round, with the 115th overall selection. He signed with the Giants, beginning his professional career in the Rookie-levelArizona League, hitting two home runs in 19 plate appearances. The Giants then promoted Williamson to the Salem-Keizer Volcanoes of the Class A-Short SeasonNorthwest League, where he hit seven home runs in 125 plate appearances. In 2013, the Giants assigned Williamson to the San Jose Giants of the Class A-AdvancedCalifornia League. He hit 25 home runs for San Jose. In 2014, he was invited to his first spring training. Though the Giants wanted to assign Williamson to the Richmond Flying Squirrels of the Class AAEastern League to start the 2014 season, an elbow injury led them to keep him in San Jose, where he could still play as a designated hitter. After beginning the season with a.318 batting average and three home runs, Williamson went on the disabled list with a torn ulnar collateral ligament of the elbow and had Tommy John surgery, ending his 2014 season. Williamson would go on to fully recover from the surgery without complication. In 2015, he began the season with Richmond and the Giants promoted him to the Sacramento River Cats of the Class AAAPacific Coast League in June. The Giants promoted Williamson to MLB on September 16, 2015. He made his MLB debut with the Giants on September 23. He made his first MLB start in right field on September 25, 2015, and got his first MLB hit off Sonny Gray of the Oakland Athletics. In 2016, Williamson began the season with Sacramento, and received a promotion to the major leagues on April 15, but was sent back to the minors a week later. On June 2, Williamson was called up after Hunter Pence suffered an injury. On June 8, 2016, Williamson hit his first major leaguehome run off David Price of the Boston Red Sox, a tie-breaking shot in the bottom of the eighth inning. During 2017 spring training, Williamson was in competition for the left field job, competing against other outfielders. He suffered a minor injury towards the end of spring training, which would cause him to miss opening day. Williamson was ping-ponged back and forth between the MLB and triple-A throughout the 2017 season and began to make large contributions to the team near the season's end, including a 3 for 3 performance with a monstrous home run against Clayton Kershaw on September 24, 2017. On March 28, 2019, Williamson was designated for assignment, after failing to make the Opening Day roster. On April 4, 2019, Williamson cleared waivers and was outrighted to Triple-A. On June 1, 2019, Williamson elected to become a free agent after clearing waivers a second time in 2019.
Seattle Mariners
On June 5, 2019, Williamson signed a minor league contract with the Seattle Mariners. The Mariners immediately selected his contract after the signing. In his first plate appearance with the Mariners, Williamson hit a 3-run home run. On July 16, he was designated for assignment and later outrighted to Triple-A. Williamson left the team on July 23, 2019, in order to pursue an opportunity in Korea.
Samsung Lions
On July 25, 2019, Williamson officially signed a $275,000 deal with the Samsung Lions of the KBO League. He became a free agent following the season.
On January 15, 2020, Williamson signed a minor league deal with the Washington Nationals. He was released on May 29, 2020.
Personal life
Williamson was born in Jacksonville, Florida on July 15, 1990. He grew up in Wake Forest, North Carolina with his three brothers, Renn, Cameron, and Christian.
