AJ McCarron threw four touchdown passes and Eddie Lacy ran for 140 yards and scored twice for the second-ranked Crimson Tide, which scored on its first three drives and cruised from there.
Alabama (13-1) became the third team to win three national titles in four seasons since polls started being used to crown champions in 1936, and the first since Nebraska from 1994-97.
Tide coach Nick Saban now has won four national championships. Only Alabama's Paul "Bear" Bryant, with six, has more.
The Fighting Irish (12-1) didn't score until they were down 35-0 late in the third quarter.