This time, the stinging jellyfish failed to appear until the final hours of her journey.
Nyad also wore a protective silicone mask and a full-body "jellyfish suit."
Asked what she would do to celebrate, Nyad said a party would begin at 7 p.m. Tuesday night, "and I expect it to go 53 hours."
President Barack Obama was among the celebrities who tweeted congratulations.
Nyad's doctor, Derek Covington, said the swimmer was healthy and would not need a long time to recover from dehydration, sunburn and the swelling in and around her mouth from seawater.
"She was incredible to watch the whole way through," he said.
Australian Susie Maroney successfully swam the route in 1997 with a shark cage, which has a drafting effect that pulls a swimmer along.
-AP