The 44-year-old's wild November ride off the shore of Nazare, Portugal beat out the previous world record, set in Southern California in 2008, by more than a foot. A panel of experts examined and measured photographs and video images of the wave to verify it, the U.K. Telegraph reported.
McNamara, a Hawaiian native, recalled that it was difficult to control his surfboard as he rode toward some rocks.
"If you fall, there's not much chance of survival," he said.
He said he hadn't even planned to go surfing that day until is friends convinced him.
"They talked me into getting on my board," McNamara said. "When I got on the board and they pulled me up with tow rope everything just felt right, it was like magic."