Republican Sen. Pat Toomey has narrowly defeated Democrat Katie McGinty.
History's most expensive Senate race concluded more than four hours after polls closed at 8 p.m. Tuesday with thousands still in line to cast their ballots.
Toomey's victory will keep Republicans in control of the Senate if GOP candidates in Alaska and Louisiana hold onto those seats, as expected.
Toomey, a former three-term congressman, was considered one of the most vulnerable Senate incumbents.
A fiscal hawk, he was seeking a second term after compiling one of the most conservative voting records in Congress. Toomey tried to distance himself from Donald Trump as he appealed to moderate Democrats and independent voters willing to split their tickets, particularly in Philadelphia's heavily populated suburbs.
McGinty, who has never held public office, was trying to become Pennsylvania's first female senator. The 53-year-old worked in Bill Clinton's White House and was recruited by top Washington Democrats to challenge Toomey.
Neither candidate had strong ties to Pittsburgh.
Toomey represented the 15th U.S. congressional district in the Lehigh Valley, while McGinty grew up in Philadelphia and worked in Harrisburg as the chief of staff to Gov. Tom Wolf and as secretary of the state Department of Environmental Protection under Governor Ed Rendell.
While Toomey argued for a repeal of business and energy regulations, McGinty touted the region's strength in engineering and university research.