[4] In 2014, Healy played for the Stockton Ports of the High-A California League, finishing the season with a .285 batting average, 16 home runs, and 83 RBI.

[7] However, Healy went on to hit .338 with 8 home runs and 34 RBI in 36 games before earning a promotion to the Nashville Sounds of the Triple-A Pacific Coast League.

He appeared in the 2016 All-Star Futures Game as Oakland's lone representative,[8][9] and earned an unlikely promotion to the major leagues on July 15.

Upon his promotion, Healy was immediately inserted by manager Bob Melvin as the team's third baseman, supplanting Danny Valencia.

[11] He recorded his first major league hit, a 3-run home run, on July 16 in a game against the Toronto Blue Jays.

On July 24, Healy hit a walk-off home run against the Tampa Bay Rays, capping a three-run ninth-inning rally.

On November 15, 2017, the Athletics traded Healy to the Seattle Mariners in exchange for Emilio Pagan and Alexander Campos.

He runs a Realty Group in the Phoenix, Arizona area, an athlete home-maintenance company, and a mobile coaching service.