Williams was charged with driving under the influence, but the jury returned the lesser verdict after a trial that lasted less than a day.
He also was convicted of driving without headlights, the offense that prompted police to stop him near downtown Denver about 3 a.m. on Nov. 12, 2010.
Williams, a defensive force for the Broncos, already is facing a six-game suspension in a separate case for failing a drug test.
He left court Wednesday with his attorney without commenting. He could be sentenced in six weeks, although it's not clear how much jail time, if any, he might serve.
Williams is scheduled to be reinstated for the Broncos' Oct. 28 game against the New Orleans Saints, although NFL commissioner Roger Goodell could punish him further for his conviction on Wednesday.
"It will be reviewed under our policies," NFL spokesman Greg Aiello said.
The Broncos said the team was aware of the situation, and it will be subject to review under the league's policies.
Prosecutors said Williams failed roadside sobriety tests during his traffic stop and refused to take a blood test to determine his possible alcohol level. He was taken to a detox facility.
During the trial in Denver District Court, Williams' attorney Harvey Steinberg questioned how the Denver police officers handled the traffic stop and criticized them for not taking into account whether concussions or other head injuries could affect sobriety tests given to Williams.
Steinberg peppered the officers during questioning about how much they remembered from the night of the traffic stop and called their testimony a "moving bullet."
He said one officer said after Williams had been taken into custody that he didn't notice slurred speech and that Williams appeared to be walking fine, contrary to what the arresting officer noted during sobriety tests.
"That's the evidence that creates the doubt," Steinberg told jurors during closing arguments.
Denver prosecutor Brian Dunn argued that Williams knew he was drunk and pointed to his refusal to take a blood test as evidence.
"I mean if you're wrongly charged, isn't that the easiest way to take care of things?" the prosecutor said.
Dunn told jurors that Williams failed sobriety testing, despite the athleticism he shows on the field.
"This is somebody who can absolutely wreck a quarterback, wreck a running back, but he can't walk a straight line," he said.
The Broncos stripped the linebacker of his team captain title shortly after his arrest -- the second time in seven seasons that he was detained for suspicion of drunken driving. In 2005, he pleaded guilty to impaired driving.
Because of his pending suspension, Williams hasn't practiced with the starters at training camp, so the team can prepare his replacement, which appears to be Wesley Woodyard.
Williams didn't do any contact work at camp until Monday when he worked with the second stringers after free agent linebacker Keith Brooking left practice with a pulled hamstring.
Williams has led the Broncos in tackles the past three seasons and five times overall in his eight years since joining the NFL as Denver's top draft pick in 2004 out of the University of Miami.
His trial was delayed several times, including after he suffered a dislocated right elbow last fall during a game. The case was supposed to be resolved in May, but a judge declared a mistrial after Williams' attorney objected to how the jury was selected.
Steinberg asked for a mistrial again on Wednesday, this time arguing that the testimony of one officer was prejudicial to Williams. At issue was the officer's answer, in response to a prosecutor's question, that sober people are not admitted into detox facilities.
Williams was expected to return to Broncos practice Thursday while the NFL reviews the outcome of the trial.