A pub owner is fulfilling his lost bet that the new trams would start running on time. (Images: Getty)

A Sydney pub that bet the city's new downtown light rail would not open and run on time will give out an estimated 30,000 free beers.

Yahoo Finance reported in November that the owner of The Morrison Bar, Fraser Short, had placed a public wager that the new George St tram line would not carry fare-paying passengers before Christmas.

This was after years of controversy and delays during construction of the now-popular mode of public transport.

"After four years of misery, broken promises and lost income, frankly we’ll believe it when we see it," Short said in November.

But the tram did open in mid-December, so it's time for The Morrison to come good on its promise.

More than 30,000 beers are expected to be poured on Tuesday when the pub hosts a Tram Party for the more than 10,000 people who registered for the bet.

The bar will also put on complimentary oysters, canapés and live entertainment at the function, to be held between 3pm and 9pm.

The Morrison's parent company The Sydney Collective has already donated $40,000 for bushfire relief, but Tram Party will also be used to raise money for the WWF Koala Crisis Appeal.

The Morrison is located near the second-last light rail stop before the tram terminates at Circular Quay.

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