He claimed to have a master's degree in education and to have played college football for three years, but checks into his background showed those statements were not true.
"Many years ago, as a young married father, I sought to pursue my dream as a football coach," he said in a statement released by Notre Dame. "In seeking employment I prepared a resume that contained inaccuracies regarding my completion of course work for a master's degree and also my level of participation in football at my alma mater. These misstatements were never stricken from my resume or biographical sketch in later years."
The 55-year-old former Georgia Tech coach signed a six-year contract Saturday night and was introduced to the media and public on Sunday.
He promised to turn around an Irish program that had become mediocre in five years under Bob Davie, fired on Dec. 2 after the Irish posted a 5-6 record after an 0-3 start. Davie's 35-25 record gave him the third-worst winning percentage in Irish history.
By Friday, though, O'Leary himself was history.
"Due to a selfish and thoughtless act many years ago, I have personally embarrassed Notre Dame, its alumni and fans," O'Leary said.
"The integrity and credibility of Notre Dame is impeccable and with that in mind, I will resign my position as head football coach," O'Leary's statement said.
His resignation was effective Thursday.
News of the resignation jolted campus at the nation's most prominent Roman Catholic university, which has used its history of football success to help it become one of the nation's premiere schools. Students studying for finals said they were embarrassed.
"It makes us look very silly that we have suffered through Bob Davie, found a coach that wasn't necessarily at the top of our priority list, and then this coach resigns over dishonesty," said Todd Engstrom, a chemistry junior from Spokane, Wash.
Notre Dame athletic director Kevin White said O'Leary's admission made it impossible for him to continue as Notre Dame coach.
"I understand that these inaccuracies represent a very human failing; nonetheless, they constitute a breach of trust that makes it impossible for us to go forward with our relationship," White said in a statement. He was not available to talk to reporters on Friday.
Casey Robin, an offensive guard for the Irish who completed his eligibility this fall, said he agreed with O'Leary's decision to resign.
"He was talking about loyalty and even honesty, and obviously he didn't live up to that expectation," Robin said. "The team needs some honesty and loyalty from a coach."
The search for a new coach will begin immediately, White said, raising the possibility he might again turn his attention to Oakland Raiders coach Jon Gruden.
With recruiting entering a dead period until about Jan. 3, there is no longer the same sense of urgency to hire a coach as there was two weeks ago.
A biography released by Notre Dame on Sunday when it announced his hiring said O'Leary received a master's degree from New York University in 1972. Sue Edson, athletic director at Syracuse, said O'Leary claimed the same thing on a biography sheet when he was hired at Syracuse as an assistant coach in 1980.
John Beckman, assistant vice president for public affairs at NYU, said O'Leary was a student there but did not receive a master's as he had claimed.
O'Leary also never earned a letter playing football at New Hampshire even though his biography says he earned three. In fact, the school said he never played in a game. Before arriving at New Hampshire, he attended the University of Dubuque for two years, 1964-66 and played on the '64 team, school officials said.
O'Leary went to New Hampshire only for two years, and never made it into a game. He said he was on the team in 1967 and 1968, but was unable to play his first year because of mononucleosis, and did not play his second year because of a knee injury.
"I can't understand how you could go all those years and not catch or correct it," former Notre Dame coach Ara Parseghian said. "That bio has been in the Georgia Tech guide for a number of years. Every year, you read your own bio and you can correct any mistakes. You add or delete things every year. All those years it was in there. How did it get in there?"
Notre Dame quarterback Carlyle Holiday was surprised by the resignation.
"It's a big shock," he said in an interview with Sporting News radio on Friday. "I never knew anything could happen like this before. (We've) just got to keep going on and find a new coach in a hurry ... try to get things going."
This isn't the first time a new Notre Dame hire has raised questions.
When Davie began in 1996, a report revealed that he had been indicted 17 years earlier for filing phony expense reports.
Davie was a 25-year-old graduate assistant for Arizona when a widespread investigation into the football program revealed that he had turned in $904 worth of airline coupons for two trips after already receiving an expense stipend.
Davie said he was just following the bookkeeping system as it had been explained to him, and he later sent Arizona a check for $1,285. He was never tried, and the charges were later dropped.