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 more than $20m (£15m) 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.