The Democratic challenger took the lead in the key battleground state by 5,587 votes on Friday morning after trailing the president since Election Day.
Prior to the latest results in Pennsylvania, Mr Biden was behind Mr Trump in the state by about 18,000 votes.
He then brought in an additional 27,396 votes to the 3,760 votes for Mr Trump in the latest batch tabulated.
Pennsylvania holds 20 Electoral College votes, a prize for either candidate to win. If Mr Biden’s lead holds, the 20 Electoral College votes will put him over the 270 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.