Ong also served as the seventh president of the Malaysian Chinese Association (MCA), a major component party in Barisan Nasional (BN); from May 2003 to October 2008.
From 1986 until 1990, Ong was the political secretary to Ling Liong Sik, the MCA president and Minister of Transport then.
After winning the 1990 general elections to be Member of Parliament (MP) of Pontian, he was appointed Parliamentary Secretary to the Ministry of Health from 26 October 1990 until 24 February 1991 by Prime Minister Mahathir Mohamad.
In January 2008, he was appointed as Acting Health Minister following the resignation of Dr. Chua Soi Lek who was involved in a sex scandal.
However, the election was marked by heavy losses for the ruling BN coalition, especially among candidates from the MCA and Malaysian Indian Congress (MIC).