Montgomery's plea agreement does not force him to cooperate with prosecutors, and his lawyers said he has no plans to testify in the trial of the other defendants, scheduled to begin on Tuesday at U.S. District Court in Manhattan.
"I sincerely regret the role I played in this unfortunate episode. I have disappointed many people, and for that I am truly sorry," Montgomery said in a statement.
The scheme involved a couple, Douglas Shyne and Natasha Singh, who are accused of receiving stolen checks, altering legitimate checks and receiving copies of checks that had been processed by bank employees, which they then counterfeited, prosecutors said.
The conspiracy involved approximately 20 checks totaling more than $5 million, prosecutors said.
In 2000, Montgomery won a gold medal as a member of the United States 4x100-metre relay team. Two years later, he set a 100m world record of 9.78 seconds, but the time was erased from the record books after the US antidoping agency found him to have received steroids. He retired from the sport immediately afterward.