Tyson quietly acknowledged to a judge that he had cocaine and was impaired when he was stopped for driving erratically in Scottsdale on Dec. 29.
He pleaded guilty to a single felony count of cocaine possession and a misdemeanor DUI count and faces up to four years and three months in prison when he is sentenced Nov. 19.
A felony charge of possession of drug paraphernalia and a second misdemeanor DUI charge were dropped, according to the terms of a plea agreement.
Defense lawyer David Chesnoff said Tyson has been clean and sober for eight months.
"It's obvious this was a crime he was committing against himself," Chesnoff said.
Police stopped Tyson after the boxer had spent the evening at Scottsdale's Pussycat Lounge. An officer said he saw Tyson wiping a white substance off the dashboard of his black BMW, and that his speech was slurred. Authorities said they found bags of cocaine in Tyson's pocket and in his car.
Tyson told officers later that he used cocaine "whenever I can get my hands on it," and that he preferred to smoke it in Marlboro cigarettes with the tobacco pulled out, according to court documents.
Since his arrest, Tyson checked himself into an in-patient treatment program for what his lawyer called "various addictions." Defense lawyer David Chesnoff had said previously that he had try to keep the boxer out of prison.
Tyson, 41, recently had been trying to revive his career with a series of boxing exhibitions.