Donaghy faces a maximum of 25 years in prison when he is sentenced for conspiracy to engage in wire fraud and transmitting wagering information through interstate commerce. He was released on a $250,000 bond.
Donaghy provided recommendations, called "picks," to co-conspirators about what team they should bet on, said U.S. District Court Judge Carol Bagley Amon. If he was correct, they paid him.
• Fast Facts: Tim Donaghy Pleads Guilty in NBA Betting Scandal
The picks included information about games that Donaghy officiated, the government said.
The information was not public, the judge said. Donaghy had "unique access," including what crews would officiate at games, the interaction of different officials and players, and the physical condition of certain players.
He concealed the scheme from the NBA and other referees to avoid detection, the judge said.
Donaghy also must pay a $500,000 fine and at least $30,000 in restitution.
Donaghy, who stood ramrod-straight, hands clasped in front of him, spoke in nearly inaudible tones as he told the judge that he is seeing a psychiatrist for his gambling addiction, and is taking an antidepressant and anxiety medication.
Prosecutors said in open court that Donaghy bet on games himself; but that was not a specific part of the verbal admission he made before the judge.
"Tim is relieved this part of the proceeding is over and we look forward to completely resolving this matter in the coming months," defense attorney John Lauro told The Associated Press after the plea. "Tim deeply regrets his involvement in this matter and especially the pain it has caused his family, friends and co-workers."
The two alleged co-conspirators, identified by prosecutors as James Battista and Thomas Martino, were in the custody of federal marshals on Wednesday and were awaiting arraignment on conspiracy charges carrying a maximum penalty of 20 years.
The judge said Donaghy concealed the scheme from the NBA and other referees to avoid detection.
The FBI first contacted the NBA on June 20 to talk about a referee alleged to be gambling on games, and the two sides met on June 21, NBA commissioner David Stern said last month. Donaghy resigned July 9 after 13 years as a referee; Stern said he would have fired him sooner but was told it might affect the investigation.
Stern blamed a "rogue, isolated criminal" for the betting scandal that threatened the credibility of every referee.
Donaghy was rated in the top tier of officials, Stern said, and there was nothing suspicious about the frequency of his foul calls. He was assigned to work in the second round of the playoffs, with his last NBA game coming during the Phoenix-San Antonio Western Conference semifinal series.
No other NBA officials or players were expected to be involved in the scandal, which Stern called the "most serious situation and worst situation that I have ever experienced either as a fan of the NBA, a lawyer for the NBA or a commissioner of the NBA."
Donaghy's next court date is Nov. 9; no sentencing date has been set.
He turned over his passport and must seek permission to travel anywhere other than Pennsylvania, Florida or New York.