After two years as an FBI agent in San Francisco and Chicago, Frederick M. Donovan returned home to launch a career that lasted decades longer.

For more than 55 years, until retiring in 2012, he maintained law offices in Brighton, not far from the Oak Square neighborhood where he grew up, and he was a familiar figure in Boston-area courtrooms.

“I admired Fred’s love for the common man, his work ethic, and how he enjoyed being a litigator,’’ said Kathleen Coffey, first justice of the West Roxbury division of the Boston Municipal Court. “He earned the respect of the judges, staff, and opposing counsel here as a man of integrity and a man of his word. And he had a wonderful Irish wit.’’

For several years in the 1960s, Mr. Donovan served as an assistant corporation counsel for the City of Boston during the administration of Mayor John. F. Collins, representing the Board of Assessors. He had previously worked as legal counsel to legislative committees in the state House of Representatives.

Mr. Donovan, who practiced civil and criminal law, and had served as a public defender, died March 7 in his West Hyannisport home of cancer. He was 91 and also lived in Brighton.

As a court-appointed attorney, Mr. Donovan appreciated the humanity and fragility of the people he defended, according to Coffey, who recalled that “he loved to try cases before a jury. He spoke clearly, had so much common sense, and was persuasive and credible.’’

Mr. Donovan also was a mentor to younger lawyers, among them Anthony Donato of Brighton.

“Fred was passionate about his clients and worked tirelessly on their behalf. He was very polished, and when he spoke, you knew he had done his homework,’’ Donato said. “He also helped out many people in need and supported worthy causes, but in a quiet way.’’

Donato said many judges appointed Mr. Donovan as a defense counsel “because they felt he would represent his client in the best way possible.’’

Another attorney, William Concannon of Brighton, said Mr. Donovan was always willing to take on tough cases and never complained, adding that “you never heard a bad word said about him.’’

Frederick Morgan Donovan was a son of Bernard L. Donovan and the former Sabina Healy. His father was a former minor league baseball player and usher/concession stand operator at Fenway Park who had been a building inspector for the City of Boston.

Mr. Donovan graduated in 1944 from St. Mary’s High School in Waltham, where he played football, hockey, and baseball, and was sports editor for the school’s yearbook committee.

He subsequently served during World War II as a third class petty officer with Navy intelligence in London where, according to his son, Fred Jr. of Chatham, he picked up several lifelong expressions.

“He never said goodbye,’’ his son recalled. “It was always ‘cheerio.’ ’’

Mr. Donovan graduated in 1950 from Boston College, where his activities included serving as junior class treasurer, and he received his law degree from Boston University in 1954, the year he was hired by the FBI.

In 1960, Mr. Donovan married Kathleen Mary Birmingham, a daughter of Leo Birmingham, for whom Birmingham Parkway at Soldiers Field Road is named. Leo Birmingham was a state representative from Brighton and House Democratic floor leader.

Kathleen, a Regis College graduate who received a master’s from BU, was an elementary school teacher and reading consultant in the Watertown system. She died in 2002.

A ward coordinator and campaign worker for Mayor Collins, Mr. Donovan ran unsuccessfully as a Democrat for state representative from the Brighton district in 1964.

In 1973, he and his wife moved to West Hyannisport, and Mr. Donovan commuted to work in Brighton and Boston.

“My father used to say when he crossed back over the bridge to the Cape his troubles evaporated,’’ his son, a freelance journalist, recalled. “When he had to stay over in Brighton, it was at his office on Washington Street.’’

Mr. Donovan, an avid Red Sox fan and season ticket holder, was also a hockey dad who drove Fred Jr. to a rink in Bourne at 5 a.m. to participate in a youth league.

The Donovans and their son also spent many hours together on the links at Cummaquid Golf Club on Cape Cod, and they took family trips to Italy and to cities across the United States.

A past president of the Ancient Order of Hibernians, Division 14, Mr. Donovan had been a member of the Massachusetts Trial Lawyers Association and the Society of Former Special Agents of the FBI.

In addition to his son, Mr. Donovan leaves a sister, Phyllis McCarthy of Brighton, and two grandchildren.

A service has been held, and burial was in Holyhood Cemetery in Brookline.

“Fred was the proper gentleman, well thought of, and a longtime part of the fabric of Brighton,’’ said Secretary of State William F. Galvin, a family friend.

Mr. Donovan also was a role model for his son.

“He had a willingness to stand for his principles, but not to take things so seriously that it would cause great stress. Loyalty was important to him. He kept in touch with the friends he grew up with in Oak Square his entire life, and he was always there for his family,’’ his son said.

His father, he added, “often told me how much he loved the law. He enjoyed the process and going to trial, and if he was able to mentor a younger attorney, that made it an even better day.’’

Marvin Pave can be reached at marvin.pave@rcn.com.