Michael Avenatti, who represented porn star Stormy Daniels in a lawsuit against President Trump, has been found guilty of attempted extortion.
The lawyer was accused of seeking to extort up to $25m (£18.9m) from Nike.
He had threatened to release information that might be harmful to the popular sports brand.
Avenatti emerged as a vocal critic of Mr Trump two years ago when he began representing Ms Daniels, and even suggested he might run for president.
He could face up to 42 years in prison.
What was Avenatti accused of?
Federal prosecutors in New York said Avenatti met a lawyer for Nike in March 2019. During their meeting, he threatened to release damaging information about Nike unless it paid him between $15m and $25m.
At the time he approached Nike, Avenatti had been representing his then-client Gary Franklin, who ran a youth basketball league in Los Angeles.
Court papers said Avenatti threatened to hold a press conference alleging Nike had made illicit payments to young basketball players in Los Angeles.
Nike immediately reported the matter to federal prosecutors. Avenatti was arrested shortly after announcing he would hold a news conference about a scandal surrounding the company.
“This was an old-fashioned shakedown,” prosecutor Geoffrey Berman said at the time.