When he was four years old, his family relocated to Singapore. His career began when he joined an insurance firm for ships. In 1975, he joined Kuo International, founded by businessman Peter Fu Yun Siak and there he met his later-to-be spouse, Christina.
After beginning his trading career at Kuo International, Ong went on to found his own firm, Hotel Properties Limited.
Today, he controls many businesses, including a few based in Bond Street in London, and his investments are worth tens of millions of dollars. He is also a well-established hotelier, having bought and built many hotels worldwide.
Ong is also credited as one of the people most responsible for bringing the Singapore Grand Prix to the country, the first Formula One night race.