The haul leaves him with $432 million (£333 million) in the bank just weeks before the November 3 election. He raised the money in conjunction with the Democratic National Committee (DNC).
The gobs of cash Mr Biden has raised since securing the nomination amount to a complete reversal in fortune for the former vice president.
To every person who chipped in a few dollars last month — thank you. Because of your support, we raised an astounding $383 million. I'm incredibly humbled.
There's still more work to be done, but I wanted to share the good news with Trimicka, one of our grassroots supporters. pic.twitter.com/f9hIPT6PTW— Joe Biden (@JoeBiden) October 15, 2020
During the Democratic primary, he struggled to raise cash and was almost broke by the time he won the South Carolina primary, which catapulted him to a commanding Super Tuesday performance.
In the months since, a flood of donations and low spending has enabled him to eclipse President Donald Trump’s once-formidable cash reserves.
Mr Biden’s campaign and the DNC raised $364 million (£280 million) in August.
In the tweet announcing his September haul, Mr Biden thanked his supporters and said he was “humbled.”
He added: “There’s still more work to be done, but I wanted to share the good news.”
The Trump campaign has not yet released their September fundraising numbers.