He took steady, measured steps Friday night for 1,800 feet on a wire across the widest part of the gorge of the roaring falls separating the U.S. and Canada, accomplishing what he said was his childhood dream - albeit wearing a tether.
"I feel like I'm on cloud nine right now," an exuberant Wallenda told reporters after his feat, which he performed before an estimated 112,000 people crowding the shores of both countries and millions more who watched a live television broadcast.
"I hope what I do and what I just did inspires people around the world to reach for the skies," he said.
He described a breathtaking view during the nighttime walk illuminated by spotlights that "compared to nothing."
"There was no way to focus on the movement of the cable," said Wallenda, 33. "If I looked down at the cable there was water moving everywhere. And if I looked up there was heavy mist blowing in front of my face. So it was a very unique, a weird sensation."
He said he accomplished the feat through "a lot of praying, that's for sure. But, you know, it's all about the concentration, the focus, and the training."
The seventh-generation member of the famed Flying Wallendas had long dreamed of pulling off the stunt, never before attempted. Other daredevils have wire-walked over the Niagara River but farther downstream and not since 1896.
"This is what dreams are made of, people," said Wallenda, who wore a microphone for the broadcast, shortly after he stepped off from a platform on the American shore.
Along the way, he calmly prayed aloud.
After passing the halfway mark, Wallenda expressed fatigue. "I'm strained, I'm drained," he said. "This is so physical, not only mental but physical."
Toward the end, as he neared the Canadian shore, Wallenda dropped to one knee and pumped his fist while the spectators cheered. He broke into a playful run about 15 feet from the finish line, where his wife and three children waited.
"I am so blessed," he said later. "How blessed I am to have the life that I have."
ABC televised the walk and insisted Wallenda use a tether to keep him from falling in the river. Wallenda said he agreed because he wasn't willing to lose the chance to perform the walk it took him well over a year to win permission from two countries to do. Such stunts are normally illegal. ABC's sponsorship helped offset some of the $1.3 million cost of the spectacle.
Wallenda said he thought about the tether, which was secured at his waist and dragged behind him, at several points along the 30-minute walk but wasn't hindered by it as he'd feared.
"Awesome! The whole thing is awesome," 8-year-old William Clements of Dresden, Ontario, said after watching the walk with his family from the Canadian side, adding he wouldn't want to walk "even over something not high."
"He was meant to do it. The weather was perfect," said Glenda Rutherford of Ontario. "It was amazing."
For Wallenda, who has grown up on the high wire and holds six Guinness records for various stunts, the Niagara Falls walk was unlike anything he'd ever done. Because it was over water, the 2-inch wire didn't have the usual stabilizer cables to keep it from swinging. Pendulum anchors were designed to keep it from twisting under the elkskin-soled shoes designed by his mother.
The Wallendas trace their roots to 1780 Austria-Hungary, when ancestors traveled as a band of acrobats, aerialists, jugglers, animal trainers and trapeze artists. The clan has been touched by tragedy, notably in 1978 when patriarch Karl Wallenda, Nik's great-grandfather, fell to his death during a stunt in Puerto Rico.
Wallenda said that at one point in the middle of the walk, he thought about his great-grandfather and the walks he had taken: "That's what this is all about, paying tribute to my ancestors, and my hero, Karl Wallenda."
About a dozen other tightrope artists have crossed the Niagara Gorge downstream, dating to Jean Francois Gravelet, aka The Great Blondin, in 1859. But no one had walked directly over the falls, and authorities hadn't allowed any tightrope acts in the area since 1896. It took Wallenda two years to persuade U.S. and Canadian authorities to allow it, and many civic leaders hoped to use the publicity to jumpstart the region's struggling economy, particularly on the U.S. side of the falls.
Associated Press Writer Jennifer Peltz in New York City contributed to this report.