In 1973, Hagan married his first wife, Jeanne Marie Carney. Carney's father, John Carney, a successful property developer and later judge, helped Hagan to get his start in Democratic politics in his brother James Carney's 1971 campaign for mayor of Cleveland.
Hagan was appointed Cuyahoga County's county recorder, but he failed to keep the seat in an election. He then ran for a seat on the Cuyahoga County board of commissioners, losing to Republican Virgil Brown. He ran again in 1981, this time successfully. Hagan served on the county commission for 16 years (1982-1998).
In 1989, Hagan made an unsuccessful attempt for the office of mayor of Cleveland, losing the Democratic primary to Ohio state Sen. Michael R. White, who went on to defeat Cleveland City Council President George L. Forbes in the general election. In 1992, with White's endorsement, Hagan made an unsuccessful bid for a seat in the U.S. House of Representatives, losing in the Democratic primary to incumbent U.S. Rep. Mary Rose Oakar.
At the end of 1998, Hagan announced his retirement from electoral politics, making self-deprecating remarks about the "twilight of [his] mediocre career."
Hagan described himself as an avowed liberal, ingrained by his father's politics, and expressed regret at the conservative trend in the Democratic Party in the 1990s. He was known to quote Camus in his speeches, a habit that did not earn him the affection of blue-collar voters. However, he allowed for compromises with his innate liberalism, agreeing to go along with government funding for the Cleveland Gateway project, which included the construction of Jacobs Field and Gund Arena.
Hagan has received praise from both sides of the political aisle. Republican Jim Petro, the state auditor and former fellow county commissioner, called him "the most honorable politician I've ever known." He even earned the friendship of former rival Forbes, who, during the 1989 election, had described Hagan as a "pimp."
Hagan ran into political trouble when it was revealed that Cuyahoga County Treasurer Francis E. Gaul (famous for saying that "Most people in Cleveland think Camus is the whale at Sea World," in reference to Hagan) had made risky investments using county funds, having assured the Board of Commissioners that the Secured Assets Fund Earnings (SAFE) fund was free of risk. Hagan was called as a witness for the defense in Gaul's trial, saying that he had "implicitly" trusted Gaul's reassurances that the investments were safe.
It was 1994, however, and the booming economy mitigated the county treasury's losses and Hagan managed to win re-election to the board of commissioners.
In 2002, he ran for the office of governor of Ohio and lost to the incumbent Republican, Robert A. Taft II, in a lopsided race that saw Hagan raising only $1.5 million compared to Taft's contribution of $9 million from his personal fortune to help his re-election.
Hagan's campaign against Taft using a duck quacking "Taftquack" raised trademark issues with the American Family Life Insurance Company's trademarked "AFLAC" quacking duck. The federal court in the Northern District of Ohio found that Hagan's commercial neither infringed nor diluted the AFLAC mark. 266 F. Supp. 2d 682.
In February 2004, Hagan announced his intention to run again for a seat on the Cuyahoga County commission against fellow Democrat and former colleague, Tim McCormack. Hagan easily defeated McCormack in the Democratic primary election and faced no Republican opposition in the November 2004 general election.
Hagan's father, Robert E. Hagan, served as a county commissioner on the board of commissioners of Trumbull County, Ohio, and in the Ohio General Assembly. Hagan's brother Robert F. Hagan is a member of the Ohio House of Representatives.
He has two daughters, named Eleanor and Marie.