The Falls span more than 1,500 feet from the United States to Canada. The drop is about 170 feet.
The stunt has been illegal for more than 100 years, but Wallenda was able to get special permission to make the attempt.
The biggest problem was making sure the wind doesn't cause the tightrope to vibrate or rotate.
Wallenda is a seventh-generation member of a circus family. His great-grandfather fell to his death from a tightrope, but 14 family members still perform various stunts.
"It's in my blood, it's just what we do as a family. My great-grandfather Karl said life in on the wire, everything else is just waiting, and it's very true for us," he said.
The stunt was televised on ABC7 at 8 p.m. PT.
Wallenda walked across without a safety net, but ABC required him to wear a harness. Wallenda said he only agreed because he was not willing to lose the chance and needed ABC's sponsorship to help offset some of the $1.3 million cost of the spectacle.