Jeremy Nowak, 66, a prominent civic investor, advocate, and commentator who founded the Philadelphia-based Reinvestment Fund, later led the William Penn Foundation, and chaired boards of organizations including the Federal Reserve Bank of Philadelphia, Mastery Charter Schools, and Alex's Lemonade Stand Foundation, died Saturday at Lankenau Medical Center of complications from a heart attack.

Mr. Nowak, of Lower Merion, suffered the heart attack July 11, said Jessica Cohen-Nowak, 31, his daughter. She was among the relatives with him when he died.

A passionate and relentless advocate for Philadelphia, Mr. Nowak had most recently been serving as a distinguished visiting fellow at Drexel University's Lindy Institute for Urban Innovation and running a consulting business. Last year, he cowrote a book about urban development, titled The New Localism: How Cities Can Thrive in the Age of Populism, and had begun traveling the country to speak with mayors about the ideas it promoted — a project his daughter said he considered his "new adventure."

His coauthor, Bruce Katz, called Mr. Nowak "a giant in community development financing, known throughout the U.S. and the world."

His dedication to solving complex community problems earned him recognition from some of the city's most important officials during his decades at the center of civic life.

Ed Rendell, the former governor and Philadelphia mayor, said he spoke to Mr. Nowak almost weekly when he led the city, calling him a "brilliant adviser and trusted by everyone."

"He understood what community development needed as well as anybody I ever met," Rendell said Saturday.

Mayor Kenney tweeted Saturday night that Nowak "made this city a better place."

John Fry, president of Drexel University, called Mr. Nowak "a ferocious advocate for the displaced and the disenfranchised."

"His greatest contribution was the way he held everyone's feet to the fire," Fry said. "He was a moral conscience."

Mr. Nowak was perhaps best known for his decades-long association with the Reinvestment Fund, which he founded with a $10,000 grant in 1985 to lend money to projects in struggling neighborhoods. By the time he left in 2011, the organization — which provided access to capital along with private-sector expertise — had allocated more than $1 billion toward housing, small businesses, and community facilities.

"Our idea was that with technical help, regular people could organize money like a community organizer does with people," he told the Inquirer in 1995, when he was named winner of the Philadelphia Award, the city's highest civic honor. "The money could be the catalyst that makes things happen."

Mr. Nowak was born in Strawberry Mansion in 1951, the son of Lillian Kovnat, a seamstress and human resources professional at the former Central Penn Bank, and Albert Nowak, a jeweler and grocer. He graduated from Central High School and, in 1973, from Pennsylvania State University, where he majored in philosophy, his daughter said. In 1986, he earned a Ph.D. in cultural anthropology from the New School for Social Research in Manhattan.

In the 1980s, Mr. Nowak worked as a community organizer in Logan, he told a PBS interviewer, but realized that "working in an inner-city neighborhood … the issue of capital was critical." Armed with a $10,000 grant, he launched what became the Reinvestment Fund, a vehicle for trying to make life better in some of the region's poorest areas.

Projects included providing loans to community groups to build housing, distributing money to struggling schools, and helping launch small businesses, such as a launderette started by Nueva Esperanza in North Philadelphia after it had been unable to find other funding to get off the ground.

"The presence [of the Reinvestment Fund] has created a consciousness of the need to provide alternative financing in the region," the Rev. Luis Cortes Jr., executive director of Nueva Esperanza, told the Inquirer in 1995. "They make things work."

After making his mark at the Reinvestment Fund, Mr. Nowak in 2011 was named executive director of the William Penn Foundation, the philanthropic powerhouse established by Otto Haas, a founder of the Rohm & Haas chemical-manufacturing company, and his wife, Phoebe, in 1945.

Mr. Nowak's tenure there lasted just 18 months, with foundation officials citing "differences in approach" over the implementation of a new strategic plan for the organization. News stories at the time said Mr. Nowak was viewed as too outspoken and aggressive at an institution known for its reserve and caution. On his watch, the foundation also attracted controversy by funding a multimillion-dollar plan to restructure the ailing Philadelphia School District by adding charter schools.

After he left the foundation, Mr. Nowak continued seeking out ways to impact the community, serving on a variety of boards in the region and, in his latest career turn, becoming a book author and consulting cities on attracting investments. He also wrote commentary for publications including the Inquirer, and chaired the Philadelphia Citizen, an online news outlet where he also served as a columnist.

"Following his career has just been kind of breathtaking to watch," said Jano Cohen, his wife of 36 years. "I was just astonished the way he would grasp a concept and information and do problem-solving."

His daughter, Jessica Cohen-Nowak, said that intellect even translated to fatherhood.

"He was someone that we sort of relied on as our North Star, our conscience for things," she said. "He was an amazing father and an amazing mentor to everyone, not just us."

In addition to his wife and daughter, Mr. Nowak is survived by his son, Adam Cohen-Nowak, 24; a brother, Edward Nowak; and a sister, Nancy Nowak.

Fry said that services would be Friday, Aug. 3, at 10 a.m. at Drexel's Behrakis Grand Hall, Creese Student Center, 3210 Chestnut Street. A reception will be on campus afterward. Details were pending Saturday.

Donations can be made to the Mastery Charter Foundation — Jeremy Nowak Scholarship; Lankenau Hospital Fund #5121 for the Cardio-thoracic Intensive Care Unit; and Alex's Lemonade Stand Foundation.