The House Ethics Committee report on former Rep. Matt Gaetz found “substantial evidence” that he engaged in sexual activity with a minor and paid women for sex, used illegal drugs and violated House rules, and state and federal laws.

The much-anticipated report released Monday outlined the committee’s findings on the years-long investigation into Mr. Gaetz, Florida Republican.

“The committee concluded there was substantial evidence that Representative Gaetz violated House Rules, state and federal laws, and other standards of conduct prohibiting prostitution, statutory rape, illicit drug use, acceptance of impermissible gifts, the provision of special favors and privileges, and obstruction of Congress,” the 42-page report says.

The panel found that Mr. Gaetz “engaged in sexual activity with a 17-year-old girl,” paid women for sex, used illegal drugs on “multiple occasions,” accepted gifts in the form of a flight to the Bahamas in 2018, had his chief of staff lie to the State Department that a woman with whom he was having sex was a constituent to get her a passport, and obstructed the panel’s investigation of his conduct.

The then-17-year-old, referred to as “Victim A” in the report, told the panel that she had sex twice with Mr. Gaetz at a party thrown by Christopher Dorworth in 2017, and at least one time “in the presence of other party attendees.” Mr. Dorworth, a lobbyist and friend of Mr. Gaetz, filed a lawsuit against Victim A earlier this year accusing her of defamation.

Victim A told the panel that she was on ecstasy that night, but was certain of her encounters with Mr. Gaetz. She received $400 in cash from Mr. Gaetz, which “she understood to be a payment for sex.” Victim A did not tell him she was a minor, nor did he ask.

Notably, the committee said that there was not enough evidence that Mr. Gaetz engaged in sex trafficking, which was central to the Justice Department’s investigation into the former lawmaker, but that he did pay for women, not minors, to cross state lines for “commercial sex.”

Still, the panel’s investigation found that Mr. Gaetz paid a dozen women “tens of thousands of dollars” that were likely in connection with sexual activity or drug use either directly, or on his behalf through Joel Greenberg, who was sentenced to 11 years in prison for underage sex trafficking and wire fraud, among other charges.

Mr. Gaetz was in a long-term relationship with at least one of the women, the report noted. She invoked the Fifth Amendment when asked about the payments.

On Monday, Mr. Gaetz again denied wrongdoing.

“Giving funds to someone you are dating – that they didn’t ask for – and that isn’t ’charged’ for sex is now prostitution?!?” he said in a post on X. “There is a reason they did this to me in a Christmas Eve-Eve report and not in a courtroom of any kind where I could present evidence and challenge witnesses.”

The investigation was pushed into new light after President-elect Donald Trump nominated Mr. Gaetz to be his attorney general. Mr. Gaetz abruptly resigned from Congress after the nomination, but many speculated that his resignation was a way to stop the release of the committee’s report because the committee typically doesn’t release reports on former members.

He pulled his name from attorney general consideration a week later.

The ethics committee secretly voted to release the report on Mr. Gaetz earlier this month after not being able to come to a consensus last month.

Ethics Committee Chairman Michael Guest, Mississippi Republican, said in a statement that he had voted against releasing the report, and stood by his position that because Mr. Gaetz had resigned from Congress last month, the panel no longer had jurisdiction over him.

“While I do not challenge the committee’s findings, I did not vote to support the release of the report and I take great exception that the majority deviated from the committee’s well-established standards and voted to release a report on an individual no longer under the committee’s jurisdiction, an action the committee has not taken since 2006,” Mr. Guest said.

Mr. Gaetz filed a lawsuit Monday against the committee in federal court to attempt to stop the release of the report, to no avail. It names the Ethics Committee and Mr. Guest as defendants. However, there were immediate issues with the filing pointed out by the court, including that it was not served to the Justice Department.

The complaint says that the committee went beyond its jurisdiction to release a report on someone who is no longer a member of Congress.

“The committee’s apparent intention to release its report after explicitly acknowledging it lacks jurisdiction over former members, its failure to follow constitutional notions of due process, and failure to adhere to its own procedural rules and precedent represents an unprecedented overreach that threatens fundamental constitutional rights and established procedural protections,” the lawsuit said.

Mr. Gaetz’s attorneys said the ethics report contains “untruthful and defamatory information” that “would significantly damage” his reputation immediately, severely and irreversibly.

The committee said that it spoke with many of the women to whom Mr. Gaetz sent money via Venmo or PayPal, and that many were cooperative at first but later became reluctant to participate over fear of his retaliation. Coupled with the Justice Department’s lack of cooperation, the panel said it “was unable to determine the full extent to which Representative Gaetz’s payments to women were compensation for engaging in sexual activity with him.”

The panel began its investigation into Mr. Gaetz in 2021, but the inquiry took a backseat when the Justice Department opened a sex-trafficking probe that lasted two years and concluded with no charges against the Florida lawmaker. The panel’s probe resumed after the federal probe ended, this time looking into some of those charges, including sexual activity with minors and graft, plus new ones of obstructing government investigations.

Throughout its years-long investigation into Mr. Gaetz, the panel sent nine requests for information, six Freedom of Information Act requests, authorized 29 subpoenas for documents and testimony, reviewed nearly 14,000 documents and contacted more than two dozen witnesses.

The panel accused the Justice Department of being uncooperative throughout its investigative process, contending that numerous requests for information were either delayed or ignored, and that the agency provided “no legal basis” for why it did not respond to a subpoena.

“To date, DOJ has provided no meaningful evidence or information to the committee or cited any lawful basis for its responses,” the report said. “The committee hopes to continue to engage with DOJ on the broader issues raised by its failure to recognize the committee’s unique mandate. As the committee has told DOJ, the committee and DOJ should be partners in their shared mission of upholding the integrity of our government institutions.”

The report outlines that Mr. Gaetz was “uncooperative” throughout the committee’s review, even after they provided written questions to Mr. Gaetz. The panel said that throughout the late spring and summer of this year, it made numerous attempts to get Mr. Gaetz to provide more information.

The former lawmaker did provide three pages of information for the committee’s initial request regarding allegations that he shared nude photos on the House floor, and “provided brief written denials of the allegations” against him, while also demanding that leaks from the normally secretive committee be addressed.

Mr. Gaetz, ultimately, ignored requests to provide exonerating information and ignored a subpoena to appear before the panel. But he did inform the panel that he would provide answers to written questions from the committee, which they obliged.

“Representative Gaetz issued his response publicly, which did not answer most questions and asserted he would ’no longer voluntarily participate’ in the investigation,” the report says.

Mr. Gaetz has continuously denied wrongdoing. In a lengthy X post last week, he blasted the panel’s decision to release the report, arguing that the Justice Department found him not guilty of the allegations against him.

He said that he would often send “funds to women I dated — even some I never dated but who asked,” but that he “NEVER had sexual contact with someone under 18,” and that any such claim “would be destroyed in court — which is why no such claim was ever made in court.”

“My 30s were an era of working very hard — and playing hard too,” said the 42-year-old Mr. Gaetz. “It’s embarrassing, though not criminal, that I probably partied, womanized, drank and smoked more than I should have earlier in life. I live a different life now.”