Miami Dolphins owner Stephen Ross unveiled a major renovation to Sun Life Stadium on Jan. 14, sitting in front of a bright, wall-sized rendering of the upgrades and telling reporters to forget about a potential referendum asking voters to approve some public funding for the project.

“I mean, that’s really not a possibility,” he said, because the team was setting a tight deadline to have a renovation agreement in place by the time the 50th and 51st Super Bowls were awarded May 22. “There’s no possibility of that happening.”

He was wrong. Less than three months later, Miami-Dade commissioners gave tentative approval to a subsidized renovation to the Miami Gardens stadium — and scheduled a May 14 referendum to give voters a say.

The special election, which will take place only if state lawmakers approve Dolphins-backed legislation, was the first of several hard-fought concessions the Dolphins would make at the request of Miami-Dade Mayor Carlos Gimenez in closed-door negotiations. Crucial details, including how much the county would pay and for how long, were not resolved until the last, dramatic two-day marathon negotiation session, according to dealmakers from both sides, who over the past two weeks recounted how the final agreement came together.

They negotiated under the political weight of recent history. The controversial deal to publicly finance most of the Miami Marlins’ new ballpark, approved without a popular vote, loomed over the talks. The Dolphins, who tried to avoid comparisons to the Marlins, and Gimenez, who doggedly opposed the baseball deal, vowed this time would be different.

In the end, the county agreed to hike the mainland hotel-tax rate to 7 percent from 6 percent and to pay the Dolphins up to $289 million over 26 years. In return, the Dolphins agreed to repay at least $112 million after 30 years, to be on the hook for up to $120 million in penalties if the stadium fails to host a certain number of major sporting events and to remain in Miami-Dade for the next three decades. If the National Football League doesn’t award Sun Life a Super Bowl next month, the entire agreement is off.

It began with the referendum — a condition Gimenez, after being asked by commissioners to sit down with the team, required before negotiations could proceed. The Dolphins, in what appeared like a strategic move to avoid the ballot box, had thought there would not be enough time to advertise and prepare an election by their self-imposed Super Bowl award deadline. But there was, because public notice for countywide elections that do not involve state or federal campaigns requires a mere 30 days — instead of 45 or 60, as the Dolphins expected.

The team agreed to the referendum in early February, with Dolphins CEO Mike Dee saying they were “never resistant” to the idea.

“We recognized the environment that was in place,” he told commissioners in April. “We recognized that the voters or the residents of Miami-Dade County had no appetite, no tolerance for anything that had taken place recently to happen again.”

THE TALKS BEGAN

Then the talks began in earnest. Miami-Dade hired financial and sports-facilities consultants. County staff toured the recesses of the stadium, where one Gimenez aide was unimpressed with its “tiny” kitchens.

A series of in-person sessions took place, mostly on Friday afternoons, in Gimenez’s offices on the 29th floor of County Hall. Ross, a billionaire real-estate developer whose business is based in New York, typically spends his weekends in South Florida.