The Democratic challenger took the lead in the key battleground state by more than 6,700 votes on Friday morning after trailing the president since Election Day.
Prior to the Friday results in Pennsylvania, Mr Biden was behind Mr Trump in the state by about 18,000 votes. Then the first batch of votes put Mr Biden in the lead, and his lead has only grown as more ballot votes come in.
Pennsylvania holds 20 Electoral College votes, a prize for either candidate to win. If Mr Biden’s lead stands, the 20 Electoral College votes will put him over the 270 electoral votes needed to take the White House - making him the 46th president of the United States.
The Associated Press has not yet called the state for Mr Biden.
About 130,000 absentee ballots in Pennsylvania have yet to be tabulated, so the count is still ongoing.
Mr Trump could still take back the lead back in Pennsylvania, but the odds remain unlikely. The absentee ballots have largely swung in Mr Biden’s favour, as he won about 87 per cent of the votes in the recent batch counted.
Throughout the Democratic primary, Mr Biden – who was born in Scranton, Pennsylvania – made the case that he alone could bring the coveted “blue wall” states back to the Democratic Party.
Michigan, Pennsylvania, and Wisconsin long went to the Democratic Party thanks to the blue-collar workers in those states. But Mr Trump won those states in 2016 against Hillary Clinton, helping give him the presidency.
Mr Biden has now re-established the “blue wall" by winning both Michigan and Wisconsin, states that were declared in his favour by the Associated Press on Wednesday, and now Pennsylvania – if his lead stands in the state.
For days the Biden campaign has insisted the numbers were showing they would win Pennsylvania. As more absentee ballots were counted, Mr Trump’s lead diminished in the state, angering the president and his allies.
Officials have long warned this could happen in states like Pennsylvania where it would take longer to tabulate absentee ballots. This is because Mr Trump’s rhetoric against mail-in votes has largely turned his voters away from the practice while Mr Biden supports have picked the voting method amid the coronavirus pandemic.
Pennsylvania’s initial vote count largely only included in-person votes before election officials started adding absentee ballots to the total, which has caused the swing from going in favour of Mr Trump to now in favour of Mr Biden.
Friday has been a monumental day for Mr Biden after days of battleground states tabulating their absentee ballots.
Besides gaining Pennsylvania, Mr Biden also took the lead in Georgia by 1,097 votes. The state has yet to be called by the Associated Press, but Mr Biden would be the first Democratic nominee to win Georgia since President Bill Clinton in 1992.
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