Ong began his professional career in 1986 at CL Computers, which he left in 1989 to join
American Express. In 1992, Ong crossed over to
Visa International, followed by
Reed Elsevier in 1995, and Planet Marketing in 1997, where he stayed on till 2007. From 2001 to 2007, Ong also worked at Publicis Groupe. Ong started RedDot Publishing Inc. which specializes in providing media solutions for the tourism industry. He was Regional Marketing Director for Visa International before he founded an integrated marketing consultancy agency which was acquired by Publicis Groupe in 2002. Since 2007, he has been serving as RedDot Publishing's managing director. The explanation offered by the Singapore media is that Ong was having an extra marital affair with 41 year-old Wendy Lim, who is also a member and grassroots volunteer of the People's Action Party. Ong's alleged affair went on for around six months before it went public after Lim's husband lodged a complaint about it. Ong's sudden retirement triggered the
Bukit Batok by-election which took place on 7 May 2016. ==Personal life==