The 54-year-old is believed to have had an affair with a grassroots activist in his ward – 41-year-old Wendy Lim.
Lim works in a logistics firm, and has been active in grassroots activities in Bukit Batok SMC, and the PAP Woman’s Wing.
The affair is believed to have gone on for half a year, and only came to light after Lim’s husband complained about it.
Ong had initially announced that he was resigning due to personal reasons.
Commenting on his resignation, Prime Minister Lee Hsien Loong said:
“David has worked hard as an MP and served his residents diligently. I thank him for his contributions. I intend to hold a by-election in the Bukit Batok SMC in due course. Meanwhile, Senior Minister of State Desmond Lee, MP for Jurong GRC, will take care of Bukit Batok residents.”
A by-election will be called for Bukit Batok SMC.
The SDP has declared its intention to contest.
The party won a quarter of the votes in General Election 2015.
In the meantime, Desmond Lee, Senior Minister of State for Home Affairs and National Development and an MP for Jurong GRC has been tasked with taking care Bukit Batok residents.