He served in that city legislative post for over twenty years climbing to the leadership position of Council President, one step below Mayor.
When David L. Lawrence resigned his post as the city's top executive to assume the governorship of Pennsylvania, Gallagher succeeded him as Mayor.
He completed and provided the final push on several of the great Lawrence projects, presiding over the opening of the Fort Pitt Tunnel among other things.
Legend has it that the mayor had to explain that the onion domes along the Monongahela River valley that Khrushchev saw were not a Potemkin Village built to impress him but the hard labor and heritage of slavs and Russian immigrants.
After stepping down as Mayor he was again elected to a term on City Council, the body that he made his biggest political impact during his life.