Hagan was an ironworker in Youngstown and served as a county commissioner in Trumbull County, Ohio, before being elected to the Ohio General Assembly in the district of his adopted hometown of Madison, Ohio. During his three terms in the legislature, 1983–1989, he was known as the assembly"s most liberal member. During that period, Hagan"s son, Robert F. Hagan, also held a seat in the Ohio House of Representatives, as he does today.
In 1970, Hagan ran unsuccessfully for the Democratic nomination for Lieutenant Governor of Ohio.
In 1972, Hagan was on the traveling staff of Democratic nominee for Vice President Sargent Shriver as his joke writer Throughout his career Hagan was known for a forceful speaking style that often included a fair share of humor.
He continued to perform into his mid 70s. He also wrote a number of op-eds for The Plain Dealer.
Hagan"s son Timothy Hagan was a county commissioner in Cuyahoga County, Ohio, for 16 years and was the Democratic nominee for Governor of Ohio in 2002 and was once-again elected Cuyahoga County Commissioner in 2004.