"We're very pleased he came forward and accepted responsibility for his actions," said Assistant U.S. Attorney Tate London.
Nickels, who smiled after the hearing and accepted hugs from well-wishers, declined to comment. He is scheduled to be sentenced before U.S. District Court Judge John Coughenour on Dec. 14.
Nickels' attorney, Jeffery Robinson, said Nickels had expressed a desire to plead guilty since he was charged.
Nickels, who had worked his way up from dealer to pit boss at the Nooksack Tribe's casino, was accused of accepting $5,000 to introduce one of the ring's alleged co-conspirators to two of his friends who were dealers at the casino, according to a federal indictment unsealed in May.
Nickels was charged at that time with one count of conspiracy and four counts of theft of funds from a gaming establishment on Indian lands.
Federal prosecutors agreed to drop the four theft charges in exchange for his guilty plea on the conspiracy charge.
The mayor said in a statement that the case has proved to be "a difficult time for our family.
"Jake today is taking an important step in accepting responsibility for his actions. Although this brings us closer to resolution, it's not over. We love him and will stand by him throughout."
