George Santos was utterly triumphant. He had just flipped a Long Island congressional seat, improbably helping deliver Republicans a House majority. It was time for a post-election shopping spree.

Over just a few days last November, Mr. Santos dropped $6,000 at Ferragamo, perhaps some of it on the red designer sneakers he later wore to walk the marble halls of Congress. He withdrew $800 in cash at a casino, where an aide said he liked to play roulette. He paid off his rent, and he pulled out another $1,000 in spending money at an A.T.M. near his apartment in Queens.

It would have been nothing for the kind of wealthy financier Mr. Santos purported to be on the campaign trail. But that was a ruse. All of it was being illegally funded by Mr. Santos’s congressional campaign, which wired him $20,000 just after Thanksgiving without ever telling campaign donors or the Federal Election Commission.

Those outlays were just a fraction of the tens of thousands of dollars or more that Mr. Santos siphoned from unknowing donors for years, propping up the kind of glittering consumer dream the 35-year-old son of immigrants never could have afforded himself, according to previously undisclosed bank records and other financial documents released by congressional investigators on Thursday.

Among the bills footed by campaign donors: trips to the casinos in Atlantic City and the Hamptons; purchases at the French fashion house Hermès; regular cosmetic treatments labeled “Botox” on internal campaign records; and even small purchases on OnlyFans, a platform best known for allowing creators to sell explicit photos and videos to subscribers.

The bipartisan House Ethics Committee report tallying them up went even deeper, unveiling new details and confirming stories by The New York Times and others about a tangled knot of biographic fictions, business frauds and bizarre campaign schemes that federal prosecutors are also scrutinizing.

But after months of investigation, the panel’s conclusion was strikingly simple: For Mr. Santos, it was all about the money.

“Representative Santos sought to fraudulently exploit every aspect of his House candidacy for his own personal financial profit,” the committee wrote in a summary of its findings. “He blatantly stole from his campaign. He deceived donors into providing what they thought were contributions to his campaign but were in fact payments for his personal benefit.”

The congressman dismissed the findings as a “biased report” designed to smear him and his family. But as the House prepared to vote again on his expulsion in the coming weeks, Mr. Santos said for the first time he would not seek re-election.

“I will not stand by as I am stoned by those who have flaws themselves,” he wrote on X, the platform formerly known as Twitter.

Mr. Santos was already facing a 23-count federal indictment, including charges that he stole from his donors and falsified campaign filings. But Thursday’s report — including hundreds of pages in previously unseen texts, emails, financial records and other documents — colored in vivid new details of the yearslong fraud.

It found that Mr. Santos appeared to have no real assets when he first decided to run for Congress as a Republican in 2019. Investigators struggled to piece together a reliable financial picture, but they said records showed only unsteady streams of income from sporadic business ventures.

He “was frequently in debt, had an abysmal credit score, and relied on an ever-growing wallet of high-interest credit cards to fund his luxury spending habits,” they wrote.

His campaigns would help change that.

Mr. Santos reported personally lending his first campaign $81,250. Most of that money was never real, but after he paid himself back using campaign contributions from donors, he walked away with $27,700 in profit, investigators found.

At the same time, Mr. Santos started directly using his campaign account — funded by small and large donors who believed they were supporting a Republican for Congress — as a personal slush fund.

Investigators found more than $40,000 in expenditures from the campaign bank account that were never reported to the F.E.C. and appear to have been used for Mr. Santos’s personal benefit, in violation of campaign finance law.

They include $1,500 in February 2022 at a business called MAX pets; smaller charges from JetBlue, Home Depot, Hilton Hotels, an urgent care office and Adventureland Amusement Park on Long Island; and more than $1,700 at two Atlantic City casinos, Caesars and Harrah’s. (A former staffer told investigators Mr. Santos said he liked playing roulette.)

Investigators flagged a July 2022 “hotel stay” for $3,332.81 that did appear on Mr. Santos’s F.E.C. filings. The problem was, Mr. Santos’s calendar showed he was in the Hamptons at the time, not engaging in any known campaign activity.

Other records show Mr. Santos charged the campaign for taxi and hotel charges in Las Vegas at a time when he told aides he was there on his honeymoon.

The report documents an even more audacious self-enrichment scheme a year later, involving a Florida company called RedStone Strategies. Federal prosecutors had already laid out the basics: Two donors gave $25,000 each to RedStone, believing it was an outside committee set up to help Mr. Santos; he pocketed the money instead.

But congressional investigators revealed for the first time what he spent it on: $4,127.80 in designer goods from Hermès; credit card bills; meals and parking; products from Sephora, the cosmetics retail giant; and purchases on OnlyFans.

Mr. Santos’s concern for his appearance evidently went beyond clothing. Records show he spent $1,500 on the campaign’s debit card just before the 2020 election at Mirza Aesthetics (motto: “Royalty Suited to Your Needs”). Nancy Marks, his campaign treasurer, described the expense as “Botox” on a spreadsheet she shared with the committee but did not disclose it to the F.E.C. And a former aide told investigators Mr. Santos once brought him to a Botox appointment “when there was a campaign event nearby.”

Mr. Santos used the card again at Virtual Skin Spa for another apparent injection in July 2022, according to Ms. Marks’s notations. And in February 2021, the campaign had made a PayPal payment for just over $1,000 to “an aesthetician associated with a spa” in the Hudson Valley. The committee said none of the cosmetic expenses had a known “campaign nexus.”

Mr. Santos and his lawyers deny financial impropriety. They have repeatedly sought to blame any wrongdoing on Ms. Marks, though the Ethics Committee said the evidence pointed firmly to Mr. Santos’s own culpability.

Despite his decision not to seek re-election, Mr. Santos is still rebuffing widespread calls for his immediate resignation.

One likely reason? For the first time in his life, Mr. Santos has a steady income, a $174,000-a-year House salary.

Michael Gold contributed reporting.