John Graass started his grueling swim at 11:30 p.m. Sunday on Catalina Island, finishing at Point Vicente in Palos Verdes 10 hours, 31 minutes and 22 seconds later on Monday, The Orange County Register reported.
He was accompanied by a friend who kayaked alongside him and by relatives and friends in another boat.
Graass told the newspaper that six hours into the swim he felt the warning signs of hypothermia.
"You're in the water for so long," he said. "It got to a point where I just couldn't stay warm anymore. I just had to suck it up."
Graass, a life guard in Newport Beach, began planning the swim about a year ago.
When he reached his goal, he pulled himself out of the water and then “just collapsed on the rocks.”
The channel was first conquered in 1927 when more than 100 people showed up to compete for a $25,000 prize. Only one, George Young, went the whole distance.