Howell, from Springville, earned $300,000.
He had a final-day total of 29-2, with the largest of his five keepers at 7-3.
"It was the best day I've ever had in 21 years of professional bass fishing, a day of a lifetime," Howell said. "I've had this dream so many times, and it's happening now. I can't believe I won the Bassmaster Classic."
Howell edged Paul Mueller of Naugatuck, Conn., by a pound.
Edwin Evers of Talala, Okla., was third at 65-11.