During his time in office, Mr. Fitzpatrick faced accusations of ethical improprieties. "It was all politics," his son said.
Mr. Fitzpatrick went on to become a well-known defense attorney representing reputed mobsters, including Raymond "Long John" Martorano, Gaeton Lucibello, Luigi "Gino" Tripodi, and Teamsters boss Frank Sheeran.
"He loved the law. He loved the whole system," said his son, who worked as an attorney with his father for more than 20 years.
NiaLena Caravasos, who joined Mr. Fitzpatrick's firm in 1997 and later became a partner, called her mentor "Captain," a reference from the 1989 Robin Williams film Dead Poets Society.
She said he insisted that "regardless of what anybody else thinks, do what's right."
When not in the headlines, Mr. Fitzpatrick was frequently seen as a panelist on the 6ABC Sunday morning public-affairs show Inside Story.
Mr. Fitzpatrick was born in Philadelphia and grew up in the city's Roxborough section. He graduated from St. Joseph's Preparatory School and then from St. Joseph's College. He received a full merit scholarship to attend the University of Pennsylvania Law School and received his law degree in 1955.
In 1956, he was hired as an assistant district attorney in Philadelphia and later served as first assistant district attorney under District Attorney James C. Crumlish Jr. from 1962 to 1966.
Crumlish was defeated by Arlen Specter in 1965, and Mr. Fitzpatrick went into private practice until he was recruited to run against the man who defeated his former boss.
In 2006, suffering from the effects of Alzheimer's disease, Mr. Fitzpatrick reluctantly retired, his son said.
"I believe his dream was to die in the courtroom after making a fantastic argument for a downtrodden client," his son said, noting that his father represented many people who never made the news.
In addition to his son, Mr. Fitzpatrick is survived by a daughter, Paula J. Fitzpatrick; another son, James Michael Fitzpatrick; and a brother.
Services are scheduled for Saturday, Sept. 6, at St. Matthias Roman Catholic Church, 128 Bryn Mawr Ave., Bala Cynwyd, with a viewing from 9 to 11 a.m., followed by a Funeral Mass at 11.
Burial will be in Westminster Cemetery, Bala Cynwyd.