Huizenga announced Friday that New York real estate developer Stephen Ross would acquire 50 percent of the franchise, Dolphin Stadium and surrounding developable land.
"We don't need some old guy limping around here trying to run this franchise," Huizenga said. "I've been in this business 18 years now. Pretty soon it'll be 24, 25. It's time for someone else to take over."
The NFL must approve the sale, which Huizenga said would be worth $1.1 billion.
Ross has an opportunity to become managing general partner in the future. Huizenga turned 70 in December, and he said his age and estate planning motivated him to make the deal.
"I will certainly be a part of this team, a partner in this team, until I die," Huizenga said at a news conference. "And after I die, my family will have the opportunity to continue owning a piece. We will be a partner for a long time."
Huizenga, the sole owner since 1994, will remain managing general partner for an indefinite period. His team is coming off a 1-15 season, the worst in franchise history.
"My heart does not want me to do this, but my head tells me it's the right thing to do," he said.
Ross is chairman of Related Companies, an international real estate development company, and he grew up in South Florida as a Dolphins fans. He said he considered buying other NFL teams in the past, but the Dolphins were his preference.
"I think the price I paid shows that," he said. "I'm a fan to start with, and I'll certainly be at the games."
Huizenga said he and Ross will be involved 50-50 in decisions.
"It's kind of like being married," Huizenga said. "No, I take it back. It's not at all like being married."
Negotiations began last April and became public in December. Speculation about a deal faded when Huizenga hired Bill Parcells as executive vice president of football operations and pledged to remain majority owner.
"Right from day one, Bill Parcells knows or knew that we were going to bring in a partner," Huizenga said. "I reminded him of that several times since he's been at the Dolphins. I met with him again this morning. Bill has no problem with it. We both are very excited about Bill being on board, and Bill will continue to report to me."
Ross said he hadn't spoken with Parcells.
"You can't help but respect the track record of Bill Parcells and what he can do for this franchise," Ross said.