The Kentucky-bred and California-trained colt broke from the No. 5 post position and gradually moved to the front of the pack before the first turn and never relinquished the lead.
American Pharoah's history-making run became complete when he held off a hard-charging Frosted in the home stretch to claim victory by 5 1/2 lengths.
Trainer Bob Baffert claimed his first Triple Crown win in his fourth attempt. He had previously come close with Silver Charm (1997), Real Quiet (1998) and War Emblem (2002) in a remarkable six-year run.
Victor Espinoza became the first Latino jockey to win the Triple Crown in his third attempt. Espinoza was aboard War Emblem as well as last year's Kentucky Derby and Preakness Stakes winner California Chrome.
The other Triple Crown winners: Sir Barton (1919), Gallant Fox (1930), Omaha (1935), War Admiral (1937), Whirlaway (1941), Count Fleet (1943), Assault (1946), Citation (1948), Secretariat (1973), Seattle Slew (1977) and Affirmed (1978).