The event was first officially recognised by Governor Lachlan Macquarie in 1810.
Sydney’s iconic building was bathed in green until 1:00am Thursday.
The manager of Tourism Ireland in Australia and New Zealand, Orla Saul, says she hopes the spirit of the occasion will rub off on Sydneysiders.
“I think it will bring a smile to their face,” she said. “Maybe they’ll have a little Irish moment.”
The Opera House is just one of many landmarks across the world to go green for this year’s St Patrick’s Day celebrations.
New York’s Empire State Building, Auckland’s Sky Tower and the London Eye will also take part in what organisers have dubbed “the green wave”.
Ms Saul says despite changes in Australia’s population, many people still have strong ties to Ireland.
“From our records, one in four people have some link to Ireland, an ancestral link, and that is still strong,” she said.
However, she says St Patrick’s Day is not just for the Irish.
“We like people just to join in even if they don’t have a link,” she said.
“St Patrick’s Day is a time when everybody can experience Irish culture, music and dance.”
The celebrations will continue on Sunday with the St Patrick’s Day Parade kicking off outside Town Hall at noon.