The debate was broadcast across the Philadelphia region on WPHL-TV.
The outcome of the race, one of the nation's most expensive, could help determine which party controls the narrowly divided Senate.
The candidates have agreed to another debate, to be held at 6abc Studios on Oct. 15.
During the combative nighttime debate Thursday, Casey tried to drive home the message that McCormick is a wealthy, carpetbagging ex-hedge fund CEO, while McCormick painted Casey as a weak, do-nothing career politician.
Casey hammered away at investments that McCormick's hedge fund made in Chinese companies, including ones the federal government came to consider part of Beijing's military and surveillance industrial complex. McCormick hit Casey as willing to vote 99% of the time with President Joe Biden and Vice President Kamala Harris.
One of the sharpest exchanges during the 60-minute debate came after Casey and McCormick agreed that they both opposed the sale of U.S. Steel to Japan's Nippon Steel.
McCormick blamed Casey for the iconic, Pittsburgh-based steelmaker canceling a $1.5 billion project for a state-of-the-art improvement to its Mon Valley Works operations after failing to get environmental permits from Allegheny County.
"This is the kind of failure of leadership that's taking Pennsylvania in the wrong direction," McCormick said.
"He was in Connecticut when that was going on, let's be clear about that," Casey shot back, referring to McCormick's time living in the Northeastern state for 12 years as a hedge fund executive. "So he doesn't have standing to talk about what should have been done in Pennsylvania."
McCormick pressed his case, saying, "We lost those jobs because of you. ... You are a weak senator, you're a liberal senator, you're a career politician who wants to have it both ways."
Casey quickly suggested that McCormick isn't strong or independent enough to defy former President Donald Trump and support a sweeping immigration reform bill that includes hundreds of millions of dollars to hire more customs agents and bolster investigations into fentanyl trafficking.
"Why don't you show some strength and support the border bill," Casey told McCormick, referring to Republican opposition that sank it after Trump said the attached immigration measures weren't tough enough.
On other topics, the candidates agreed on the need for tariffs to protect certain industries, such as steel and aluminum, while not seeing eye to eye on the Senate filibuster.
Casey supported getting rid of the filibuster, saying it is preventing votes on things like women's, voters' and unions' rights, legislation he said McCormick would oppose. Senators should be voting on the "big issues and fulfill the wishes and aspirations of those who voted for us," he said.
McCormick countered that the filibuster protects moderation.
"We shouldn't have extremes on either side," McCormick said.
McCormick also said he supports Trump's pledge to carry out a mass deportation of immigrants in the country without permission - prioritizing people with criminal records - and insisted he would protect Social Security and Medicare while backing the extension of tax cuts passed under Trump.
Casey accused McCormick of wanting to extend those cuts to give a break to the same billionaires donating to campaign.
Casey, 64, perhaps Pennsylvania's best-known politician, is seeking a fourth term and is facing what he calls his toughest reelection challenge yet. A staunch ally of labor unions, former state auditor general and treasurer and Pennsylvania's longest-serving Senate Democrat, he has campaigned on preserving the middle class, abortion rights, labor rights and voting rights, all of which he says McCormick and Donald Trump pose a threat to.
McCormick, 59, is making his second run for the Senate after losing narrowly to Dr. Mehmet Oz in 2022's Republican primary. He is a former hedge fund CEO who served at the highest levels of former President George W. Bush's administration and sat on Trump's Defense Advisory Board.
Both Casey and McCormick were uncontested for their party's nominations in the primary election.
Also on the Nov. 5 Senate ballot are John Thomas of the Libertarian Party, Leila Hazou of the Green Party and Marty Selker of the Constitution Party. They were not invited to the debate.
The Associated Press contributed to this report.