[3][4] After high school, Gainey attended Norfolk State University for a semester before returning home to Pittsburgh, where he would transfer to the Community College of Allegheny County.

[5] Early on in his career, Gainey spent six years as a legislative aide to Pennsylvania State Representative Joseph Preston Jr.[6] Gainey's early career also included a period as a special projects manager under Pittsburgh Mayor Tom Murphy.

[7] Gainey later took a position with the City of Pittsburgh under Mayor Luke Ravenstahl in a community development role.

[14] Gainey's opponents included incumbent mayor Bill Peduto, who was running for re-election after two terms in office.

[16][17][18] Gainey attacked Peduto's performance over his two terms as mayor, accusing the incumbent mayor of failing to pursue tax payments from nonprofit healthcare giant UPMC and of squandering an opportunity to improve police–community relations after the shooting of Antwon Rose.

[23] On January 22, 2016, Gainey's younger sister, Janese Talton-Jackson, was shot dead in Pittsburgh's Homewood neighborhood by a man who followed her out of a bar.

[28] Incumbent District Attorney (DA) of Allegheny County, Stephen Zappala, argues that the Office of Mayor Gainey has failed to properly enforce police practice.

[30] Gainey has pledged to pass a lead ordinance, not privatize PWSA, and work with environmentalists to develop a plan to address climate change.

The proposal contains provisions to quadruple the funding allocated to bridge management as well as a 136% increase in traffic relieving amenities.