The Denver County panel also found the eight-year NFL veteran guilty of driving without his headlights on in a case triggered by a Nov. 12, 2010, arrest for driving under the influence, The Denver Post reported.
Driving while ability impaired is a lesser offense than DUI.
The verdict came three months after Williams, 30, was granted a mistrial in the case on the grounds there were mistakes during jury selection, the newspaper said.
Police said Williams refused to submit to a blood or breath sample when he was pulled over on a Denver street for driving without his headlights on.
The arresting officers said the former first-round draft choice out of Miami-Florida failed a series of roadside sobriety tests.
Williams is already facing a six-game suspension for failing a performance-enhancing test during last year's training camp and could receive more NFL sanctions after Wednesday's verdict, the Post reported.