After leaving the Maryland Senate he became a District Court judge and heard cases throughout the state until September 2012.
He was born in Hampden and raised in Halethorpe. His father, John Edward Coolahan, was a tax assessor and a Baltimore Transit Co. worker. His mother, Blanche Zimmerman, worked in the Hampden textile mills.
"My grandmother was from Hampden and grandfather from Pigtown. They were both very proud of their roots," said his son Bill. "My father got his colorful side from his mother, who was a flapper during the 1920s and bobbed her hair and drove a car as a young woman."
He was a 1950 Mount St. Joseph's High School graduate, where he played football. He enlisted in the Marines and received a Purple Heart during combat in the Korean War.
He earned a degree at what is now McDaniel College and worked as a home improvement inspector for the state while putting himself through the University of Baltimore School of Law. He later owned and operated an Arbutus filling station. A mechanic, he often washed his constituents' windows and pumped their gas.
"Politics was in the family," his son Bill said. "His father, who ran for office unsuccessfully, served as his secretary in Annapolis. They didn't always get along. My father fired him more than once."
Judge Coolahan was an early proponent of a Maryland lottery.
"I led the forces against it," said a friend, former state Sen. Julian L. Lapides, who lives in Bolton Hill. "He led the forces for it. John was tough and honest, and represented his constituency well."
Judge Coolahan served in the House of Delegates from 1967 to 1970 and in the Maryland Senate from 1971 to 1978 and again from 1983 to 1986. He was Baltimore County delegation chair for several years.
The Southwest Baltimore County Democrat was described as a "sometimes gruff, almost always direct politician whose distinctive tawny mane has thinned and turned to silver" in a 1994 Baltimore Sun profile.
"I've always liked politics — it's an advocation rather than a vocation — and I think my conservative views are more in line with the voters of this county than those of the other candidates," he told a reporter that year.
The news account said Judge Coolahan acquired the "Lion of Halethorpe" handle from a 1976 Evening Sun article "when he led a six-day Senate filibuster in an attempt to defeat funding for the subway. The nickname stuck."
He left political office in 1989 when Gov. William Donald Schaefer appointed him to the District Court.
"They both had hot tempers, but they could both sit down and have coffee later," said his son. "Politics to them was getting the job done, not promoting yourself."
Judge Coolahan ran unsuccessfully for Baltimore County executive twice. In the 1978 primary, he placed second in a close race behind Democrat Donald P. Hutchinson, who was elected in the general election. Mr. Hutchinson made him a Baltimore County lobbyist, but Judge Coolahan soon resigned when the county's needs conflicted with his opposition to government money being spent for the Baltimore Orioles.
In a second try for county executive, he ran third behind C.A. Dutch Ruppersberger in the 1994 primary.
"The solitary figure prowling Oregon Avenue with an armful of brochures drew honks from motorists and caused pedestrians to dart across the street to shake his hand," said a 1994 Sun profile. "People stopped their mowing or gardening, mopped their brows and hurried to greet him. This is lion country. Halethorpe-Arbutus. The political turf of John Carroll Coolahan, the Lion of Halethorpe."
Joseph Bartenfelder, a former Baltimore County councilman and member of the House of Delegates, recalled that people would always listen to what Judge Coolahan had to say.
"John was a good leader for the people of Baltimore County even though he was always associated with Halethorpe," said Mr. Bartenfelder, who lives in Baltimore County.
Mr. Bartenfelder also recalled Mr. Coolahan's fiscal conservatism and policy of opposing what he thought were expensive state projects.
"People would sometimes say, 'John, Are you for anything?' " he said.
A funeral Mass will be held at noon Friday at the Roman Catholic Church of Ascension, 4603 Poplar Ave. in Halethorpe, where he was a member.
In addition to his son, survivors include his wife of 57 years, the former Joanna Sakievich; three other sons, Michael J. "Mike" Coolahan of Halethorpe, James P. "Jim" Coolahan of Ellicott City and Daniel Carroll "Danny" Coolahan of Arbutus; a daughter, Kathleen Coolahan of Halethorpe; a brother, Donald Coolahan of Orlando, Fla.; 12 grandchildren; and a great-granddaughter.