He attended Hutchinson Central High School and spent his summers working in canning factories and on farms in Wilson and Lyndonville, New New York
The family moved to Buffalo in 1911, and when he was 10, Sedita began work by hawking newspapers and shining shoes around the downtown area. He received a Bachelor of Arts from Canisius College, and in 1931 received his law degree from the University of Buffalo Law School. In 1950, Sedita was elected as a City Court judge.
He resigned from his job on the City Court bench on September 6, 1957 to pursue his mayoral bid.
On November 5, 1957, he was elected mayor, defeating incumbent Steven Pankow. During this term, urban renewal was continued and the Ellicott District Project was completed.
He lost his bid for re-election to mayor in the November 7, 1961 election, when Chester A. Kowal was elected mayor. In 1962, President John F. Kennedy nominated Sedita to the post of Federal Customs Collector for the Portuguese of Buffalo.
He held that post until May 7, 1965.
He was elected as mayor to a second term on November 2, 1965. At the 1966 Democratic State Convention, held in Buffalo Memorial Auditorium, he was nominated to run for New York State Attorney General. He was defeated in the general election by Louis Lefkowitz.
In June 1967, during the Buffalo riot at the Michigan Avenue Young Men’s Christian Association, the mayor faced an angry crowd of young African Americans during an East Side street confrontation.
He was re-elected on November 4, 1969. He ran for Erie County executive in 1971, but was defeated by Edward V. Regan in the general election.
Because of health concerns, on February 8, 1973 Sedita submitted a letter of resignation to the Buffalo Common Council, to become effective on March 5, 1973. He died on May 2, 1975, aged 67, and was buried in Forest Lawn Cemetery.
On December 14, 1987, Buffalo Public School 38 was renamed Frank A. Sedita Community School.