Williams was punished for violating the NFL's substance-abuse policy following his August conviction of driving while ability impaired.
Williams 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 Broncos' leading tackler in four of the last five seasons, won't be eligible to return to the team until Nov. 12.
One Broncos source told NFL Network reporter Michelle Beisner that they "knew additional discipline was a possibility and had been preparing for an extended suspension."
Williams originally was scheduled to return in time for the Oct. 28 game against the New Orleans Saints, but he'll now miss that game and road contests at Cincinnati and Carolina, too.
Wesley Woodyard and Keith Brooking have shared snaps at weakside linebacker in Williams' absence.
Williams met with NFL 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.
Williams originally was charged with driving under the influence, but a jury returned a conviction on a lesser charge. Williams 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.
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.
The Associated Press contributed to this report.