Before Mr. Edgar came along, the county had sent a long string of Republicans to Congress since the Civil War, interrupted by Democrats for just one two-year term during the Gilded Age and another during the Great Depression.
A young chaplain at Drexel University, he set out to end that string, campaigning around the district in a Volkswagen Beetle.
"It was literally the man against the machine," remembered David Landau, the Delaware County Democratic chairman, who stumped for Mr. Edgar and was the party's candidate for the same seat in 1990. "He was a phenomenon."
In later years, Mr. Edgar acknowledged that he had run at the right time - an antiwar candidate when the nation was exhausted by Vietnam, and amid a voter rebellion that sent scores of young Democrats to Congress in reaction to the scandals of President Richard M. Nixon's administration.
Then Mr. Edgar hung on in a district where registered Republicans outnumbered Democrats by as much as 3-1. The GOP organization came at him hard, with well-funded candidates. In 1984, Mr. Edgar squeaked past Curt Weldon, who later would succeed him, by a few hundred votes.
"He was independent," Landau said. "Long before we talked about ticket-splitting Republicans in the suburbs, he was proving it."
In the House, Mr. Edgar was known for railing against the pork-barrel spending on highways, dams, and other public-works projects often tucked into legislation. He championed environmental issues, and was a leader in pushing for more mental-health treatment for returning Vietnam veterans, and for the government to recognize illnesses from exposure to Agent Orange.
"He was a hero to me," said Joseph M. Manko, a Bala Cynwyd environmental lawyer and Democratic fund-raiser who was finance chairman for four Edgar campaigns, including the 1986 Senate run.
"He was the most humble, honest, forthright politician I've ever come across," Manko said Tuesday. "He hated to ask people for money."
Mr. Edgar had been president and CEO of Common Cause since 2007, traveling the country to campaign to limit the influence of big money in politics and for more transparency in government. He called for a constitutional amendment to stop the flood of corporate and super PAC money in the wake of the Citizens United Supreme Court decision of 2010.
"We are deeply saddened and shaken today by the passing of Bob Edgar," Common Cause chairman Robert Reich, a former U.S. labor secretary, said in a statement. "Bob will be remembered for his decency, kindness, compassion, and humor."
After leaving Congress, Mr. Edgar was president of the Claremont (Calif.) School of Theology for 10 years. He served as secretary-general of the National Council of Churches from 2000 to 2007.
"He was always trying to make the world a better place for all human beings," Merle Edgar said.
Along with his wife, Mr. Edgar is survived by sons Andrew, David, and Rob.
Mr. Edgar was born in Philadelphia in 1943 and grew up in Springfield, Delaware County. He graduated from Lycoming College in Williamsport, Pa., and received a master's of divinity at Drew University in Madison, N.J.
Two years before he ran for Congress, Mr. Edgar helped found the People's Emergency Center, a nonprofit social services agency for homeless families.
"He had a heart for people," Rep. Chaka Fattah (D., Pa.) said. "He will be missed, not just by his family, but by the thousands whose lives he touched - mine included."
Contact Thomas Fitzgerald
at 215-854-2718, firstname.lastname@example.org,
or follow on Twitter @tomfitzgerald. Read his blog, "The Big Tent," at www.philly.com/bigtent.