Williams was punished for violating the league's substance abuse policy following his conviction in August of driving while ability impaired.
He already was serving a six-game suspension to start the season for violating the league's banned-substances policy -- such as performance enhancing drugs -- after the NFL said he supplied a "non-human" urine sample during a drug test.
Williams, the team's leading tackler in four of the last five seasons, won't be eligible to return to the Broncos until Nov. 12.
He was originally slated to return in time for the game against New Orleans on Oct. 28, but will now miss that game and road contests at Cincinnati and Carolina, too.
The Broncos, who had been preparing for Williams' suspension to be extended, declined comment after arriving in New England on Friday night for their game against the Patriots this weekend.
Williams met with commissioner Roger Goodell in New York last month in hopes of avoiding further punishment from the league following his latest run-in, a case that stemmed from a drunken driving arrest nearly two years ago.
He was originally charged with driving under the influence, but a jury returned a conviction on a lesser charge. He was also convicted of driving without headlights, the offense that prompted police to stop him near downtown Denver about 3 a.m. on Nov. 12, 2010.
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.
The Broncos stripped Williams of his captaincy shortly after his arrest -- the second time he'd been detained for suspicion of drunken driving. In 2005, he pleaded guilty to impaired driving.
Williams has led the Broncos in tackles five times in his eight years since joining the NFL as Denver's top draft pick in 2004 out of the University of Miami.