The House Ethics Committee said on Monday that its lengthy investigation had found that former Representative Matt Gaetz, Republican of Florida, President-elect Donald J. Trump’s initial choice for attorney general, had regularly paid women for sex, had sex with an underage girl and used illegal drugs.

The report was released weeks after Mr. Gaetz withdrew from consideration to be the nation’s chief law enforcement officer and resigned from Congress, and after years in which he had spawned enemies on both sides of the aisle with his bellicose political style.

Mr. Gaetz has denied any wrongdoing.

The panel found that from at least 2017 to 2020, Mr. Gaetz “regularly paid women for engaging in sexual activity with him.” The report said that in 2017, Mr. Gaetz had “engaged in sexual activity with a 17-year-old girl,” who was paid.

From 2017 to 2019, the report said, Mr. Gaetz used or possessed illegal drugs, including cocaine and Ecstasy “on multiple occasions,” and accepted lavish gifts, including transportation to and lodging in the Bahamas, in excess of permissible amounts.

“Representative Gaetz has acted in a manner that reflects discreditably upon the House,” the report stated.