In a news release Friday, Biden's campaign says he raised the money from nearly 97,000 individuals across all 50 states, including 65,000 who weren't solicited by email.
Biden edged former Texas Rep. Beto O'Rourke's first-day total of $6.1 million and Vermont Sen. Bernie Sanders' sum of slightly less than $6 million.
Biden attended a fundraiser in Philadelphia on Thursday evening aimed at raising $500,000. Hosts said Friday that the event raised substantially more.
The former vice president under Barack Obama entered the race Thursday, declaring the "soul of this nation" at stake under President Trump's administration.