The financial assistance, which is believed will be handed out over three years, is understood to have come from the Northern Ireland Assembly.
United was reportedly expected to axe the route next month, according to the BBC, believing that it would be more profitable to base its aircraft elsewhere.
The managing director of Belfast International airport, Graham Keddie, said: "Two weeks ago we had lost it.
"It was a Northern Ireland team effort to get it back."
Economy minister Simon Hamilton said the executive had backed the rescue package.
"It is public money being spent to ensure we keep this very important route in place," he added.
He said the route was crucial to attracting US-inward investment.
DUP MP for North Antrim Ian Paisley said: "Losing this route would have been a blow to the prestige of Northern Ireland.
"Imagine the outcry if this had been lost."
