Pitino and his family arrived to enthusiastic cheers at an evening news conference and pep rally to introduce him as coach.
"Now it's my time to lead the Cardinals back to prominence," Pitino said.
His hiring at Louisville follows a bold, aggressive courtship by athletic director Tom Jurich, who acted as a one-man search committee. Jurich said two weeks ago that Pitino was his only candidate for the job.
Pitino, who was courted by Michigan and other schools, said wife Joanne helped convince him to take the Louisville job.
He said she told him, "I think that you love the state of Kentucky; you love the people you met at U. of L. I think you should go back to the place you love."
He said he almost decided to take the Michigan job Wednesday morning.
Jurich flew to Pitino's Miami home on March 9 and persuaded him to visit the Louisville campus last week.
Pitino left impressed, but said he wanted to consult his family before making a decision. He worked the NCAA Midwest Regional in Dayton, Ohio, as an analyst for CBS before flying to Boton to meet his family Sunday night.
Pitino replaces Hall of Fame coach Denny Crum, who retired after months of strained relations with Jurich. The 64-year-old Crum, who led Louisville to NCAA championships in 1980 and '86, had two seasons left on his contract, but accepted a $7 million buyout.
Speculation began immediately that Pitino was Jurich's top choice, and even former Louisville players voiced support.
Jurich called a news conference March 6 to confirm he was pursuing Pitino. When Pitino expressed interest, some Kentucky fans said they were angry that Pitino would even consider coaching the Wildcats' rival.
Pitino said the opinions of Kentucky fans factored into his decision but that his family mattered most. His 18-year-old son, Richard, accompanied him during his recent visit to the Louisville campus.
Pitino, 48, took the Celtics' job in 1997 after eight seasons at Kentucky that solidified his reputation as a master rebuilder. He previously turned around mediocre programs at Boston University and Providence, guiding both to the NCAA tournament. He also coached the New York Knicks from 1987-89.
The season before Pitino arrived at Kentucky, the team went 13-19 its first losing record in 62 years and was hit with NCAA probation. He inherits a Louisville program in similar disarray.
The Cardinals finished this season 12-19, capping the worst four-year run in Crum's 30 years. Louisville is 62-62 since reaching the NCAA regional finals in 1997 and was twice put on probation in the 1990s.
The school hopes Pitino can guide the Cardinals back to the national prominence they enjoyed in the 1980s.
It took Pitino three seasons to do it in Lexington. Kentucky went 14-14 in his first season and 22-6 in his second.
In his third, the Wildcats went 29-7, losing to Duke in the memorable 1992 East Regional final.
Kentucky reached the Final Four the following season and went 124-19 over the next four, winning the school's sixth national title in 1996. The Wildcats reached the title game in 1997, losing to Arizona, before Pitino accepted a 10-year, $50 million contract to coach the Celtics.
Pitino turned the Wildcats over to Tubby Smith, a former assistant. Smith congratulated Louisville from Philadelphia, where Kentucky is preparing to play Southern California on Thursday in the East Regional semifinals.
"They're getting one of the great coaches in basketball," Smith said. "I'll welcome him back."
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