With 96% percent of the expected vote counted, Biden has a lead of 30,900 votes over President Donald Trump in the Keystone State.
Four years ago, President Donald Trump breached the Democrats' "blue wall," narrowly winning Pennsylvania, Michigan and Wisconsin - a trio of Great Lakes states that had long served as a bulwark against Republican presidential candidates.
On Saturday, Democrat Joe Biden captured it back - and also won the presidency.
ABC News and the Associated Press called the race for Biden, who held a 34,243-vote lead, after it determined that the remaining ballots left to be counted would not allow Trump to catch up. Biden was already declared the winner in both Michigan and Wisconsin.
Biden held a .51 percentage point lead late Saturday morning. Under Pennsylvania law, a recount is automatic when the margin between two candidates in a statewide race is less than 0.5 percentage points. Biden's lead over Trump was on track to stay outside of that margin as final votes are counted.
There are roughly 62,000 mail ballots remaining to be counted. Biden has won the overwhelming majority of mail ballots cast in the state.
Biden's win in Pennsylvania was a dramatic, though not unexpected, turn after Trump jumped out to an early Election Day lead of 675,000 votes and prematurely declared he had won the state.
Over coming days, as local elections officials tabulated more ballots, Trump's lead dropped sharply, with Biden winning roughly 75 percent of the mail-in vote between Wednesday and Friday, according to an analysis by the AP.
Another reason the late-breaking mail vote broke Biden's way: Under state law, elections officials are not allowed to process mail-in ballots until Election Day.
Biden, who was born in Scranton, claims favorite-son status in the state and has long played up the idea that he was Pennsylvania's "third senator" during his decades representing neighboring Delaware. He's also campaigned extensively in the state from his home in Delaware.
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The Associated Press contributed to this report.