[1] Ong was educated at Anglo-Chinese School (Independent) and National Junior College, before being awarded the Singapore Armed Forces (SAF) Overseas Scholarship in 1994 to study at the London School of Economics, where he graduated with a Bachelor of Science with second class honours degree.

Ong enlisted in the Singapore Armed Forces (SAF) in January 1994 and was commissioned as an infantry officer in October that year.

Ong has held various appointments in the SAF, including the Commander of the 7th Singapore Infantry Brigade from 2010 to 2011, and Head of the Joint Plans and Transformation Department.

[4] He succeeded Perry Lim as Chief of Army on 14 August 2015,[2][5] and was promoted to the rank of Major-General on 1 July 2016.

Ong was appointed Chief of Defence Force on 23 March 2018,[7] and was promoted to the rank of Lieutenant-General on 1 July 2018.