The Democrat won November's contest with 306 electoral college votes to Republican Donald Trump's 232.
Under the US system, voters actually cast their ballots for "electors", who in turn, formally vote for candidates weeks after the election.
Despite this process, President Trump is not expected to accept the result.
Normally the electors do not get that much attention but this year, due to Mr Trump's persistent efforts to question and overturn the results - involving legal challenges which have been rejected by courts across the country - the state-by-state vote was in the spotlight.
Solidly Democrat California, with its 55 electors, was one of the last states to vote on Monday and took Mr Biden across the 270-vote threshold required to win the presidency.
Heightened security had been put in place in some states, including Michigan and Georgia, ahead of voting, which took place in state capitals and Washington DC.
In Michigan - a key swing state which Mr Biden won - legislative offices in the state capital Lansing were closed due to "credible" threats of violence.
The vote at the capitol building went ahead peacefully although a group of Republicans tried to enter the building to hold their own vote and were turned away.
"The people have spoken. It was a safe, fair and secure election," said Governor Gretchen Whitmer, a Democrat who had been the subject of a kidnapping plot thwarted by the FBI earlier this year. "After today, the results will be final."