Vice President Kamala Harris’s campaign set a record for the biggest fund-raising quarter ever this fall, raising $1 billion in the three-month period that ended Sept. 30.

Ms. Harris’s campaign and its allied party committees raised over $359 million in September alone, compared with the $160 million reported by former President Donald J. Trump’s campaign and allied groups.

Ms. Harris and her groups entered October with over $346 million on hand; Mr. Trump’s aides said his campaign and its affiliated groups had $283 million.

The vast gap between Ms. Harris’s and Mr. Trump’s committees was laid bare in new filings made with the Federal Election Commission on Sunday evening. The figures show the state of the race as of the end of September, and they capture the fallout of the presidential debate that month, which Ms. Harris was widely perceived to have won.

The figures may be new but the story is familiar.

Each month since Ms. Harris became the Democratic presidential nominee, she has significantly out-raised and outspent Mr. Trump, building a vastly bigger campaign than has the Republican nominee.