The son of a career military officer, Bob Cranmer was born in Pittsburgh, where his parents settled after his father retired from the United States Army. He grew up in the suburb of Brentwood, where he still resides with his wife, Lesa. He graduated from Brentwood High School in 1974 and Duquesne University in 1978, at which time he was commissioned as a second lieutenant of military intelligence in the regular army. He went on to serve various assignments with the 101st Airborne Division and in Washington, D.C. Leaving the army in 1986, Bob went to work for AT&T and returned to Pittsburgh.
Entering politics, he was elected Allegheny County Commissioner in 1995 and served as chairman of the board. Working with a fellow commissioner and the mayor of Pittsburgh, Bob was instrumental in the implementation of a major development plan for Pittsburgh, subsequently called Renaissance III. It involved significant redevelopment downtown, construction of two new sports stadiums, and a new convention center. Bob currently runs a firm providing local, state, and federal government relations.