Felipe Massa: "While we have three night races, Singapore is the only one in the middle of the city, in the middle of the night, and it's great".
The cost of hosting the race around the Marina Bay Street Circuit was estimated to cost around $150 million each year, although Mr Iswaran said costs had come down by about $15 million a year.
F1 chairman Chase Carey said he was thrilled about the new contract.
Mercedes have clawed back Ferrari's lead in recent weeks, but Vettel will fancy his chances here, having won four of the last six Singapore Grands Prix.
Essential to building the world's fastest vehicles, Formula One technology has been sought-after by various global industries and is closely monitored by racing fans who attend the annual Singapore event, which was Asia's first-ever street circuit.
Singapore has considerable appeal as a popular tourist destination, with about "40 to 50 percent of visitors (to the race) from overseas", said Lionel Yeo, the chief executive of Singapore's tourism board.
Despite the Marina Bay circuit being one of the most hard tracks, Williams head to Singapore hoping for a "good result" under the lights.
In a statement, Formula One said: "Since its debut in 2008, the first ever night Grand Prix is one of the highlights of the F1 calendar and one of the most attractive and spectacular races".
With this year's race taking place on Sunday, the event could have received no better boost than confirmation it will continue until at least 2021.