Joan Carter, a businesswoman who was among the first women admitted to the elite club, received the gavel at a ceremony at the league's landmark building downtown. She was unopposed in the election held Monday.
With oil portraits of male past presidents hanging all around her, Carter told hundreds of members that the league she is inheriting is a much different place than the one she joined 25 years ago. She later described the club as having a more vibrant and inviting environment.
"At that time, being a woman member, you thought of yourself as a woman member," Carter, 67, told The Associated Press. "Now we just think of ourselves as members."
Like many private social clubs, the 148-year-old Union League was long seen as the exclusive bastion of wealthy white males until admitting its first black member in 1974. Carter was in the first cohort of women admitted in 1986.
That it's taken nearly 25 years for the league to have a female leader is part of "a natural evolution of what has been occurring in our culture," said Susanne Wegrzyn, president and CEO of the National Club Association, a Washington-based advocacy group for private clubs.
Still, only about 6 percent of clubs in the association's database have female presidents, Wegrzyn said. She said a higher percentage are in other governance roles and estimated women comprise 20 percent of private club members overall.
At the Union League, where initiation costs $3,600 and annual dues are $4,000, about 15 percent of members are female, said general manager Jeffrey McFadden. But women make up 40 percent of new members, he said.
McFadden described the league as a place for business people and civic leaders to connect, like "a country club without a golf course in the middle of center city Philadelphia." He said the 3,200-member organization is increasingly family-oriented and not the "rich men's lunch club" it is often perceived to be.
Jackets, though, are still required at the league's stately building, which takes up most of a city block and often hosts U.S. presidents, dignitaries, entertainers and heads of state. It is one of the nation's oldest private clubs.
In a toast at Tuesday's luncheon, former league President Frank Giordano said that "our message today is that we are an exclusive club, but we are inclusive."
New Jersey state Sen. Diane Allen, who joined the league with Carter, reminded guests in later remarks that even after women were admitted to the club, they were not allowed in the billiards and cards rooms.
That is until Carter wrote a letter to league officials suggesting that women's membership dues be reduced to compensate for their partial use of the facilities. The rooms were soon opened to all members.
Allen described the new president as a shrewd businesswoman with an engaging personality, calling her "the best one for the job."
"I know she's going to lead us into a wonderful future," Allen said.
Carter is co-founder and president of New Jersey-based UM Holdings Ltd., a private equity investment firm, and a former chairwoman of the board of directors at the Federal Reserve Bank of Philadelphia. She joined the league at the urging of her husband, who is her business partner and a club member.
Carter stressed the league's patriotic heritage and motto, "Love of Country Leads." She noted it holds one of the nation's largest collections of Civil War-related documents, statues and artifacts, which the club plans to display publicly in a new heritage center opening in April.
Shepherding the completion of that exhibit is one of Carter's top priorities when she takes office Jan. 1. She also is preparing for the league's celebration of its 150th anniversary in 2012.
After its founding in 1862, 226 other Union Leagues formed around the country. Today, only three are left, in Philadelphia, Chicago and New York.