Koh joined Gerakan in 1982. He won a parliamentary seat during the 1982 general election but lost it to Lim Kit Siang in the following 1986 general election. The following year, he was elected Gerakan Youth chairman. Koh was the protégé of then Penang Chief Minister Lim Chong Eu, serving as Lim's political secretary and chief aide from 1986 to 1990.
Gerakan leadership
Koh became a vice-president of Gerakan in 1991 and later deputy president in 2005. On 8 April 2007, following the retirement of long-serving president Lim Keng Yaik, he took over the presidency in an acting capacity. He was formally elected president in 2008.
Penang Chief Minister
In the 1990 general election, Chief Minister Lim Chong Eu lost his state seat. Koh, who was a first-term state assemblyman from Tanjung Bungah, was selected to lead the Barisan Nasional government in Penang, and became the state's third Chief Minister. Koh served four terms as Chief Minister for a total of 18 years from 1990 to 2008. In the 1995 general election, he was challenged in his state seat by Lim Kit Siang, who unseated the previous Chief Minister Lim Chong Eu in 1990. Koh beat Kit Siang with over 70% of the votes. He stepped down in 2008 to contest the Batu Kawanparliamentary seat during the general election. Koh was said to be pressured into leaving his position as Chief Minister to join federal politics. He eventually lost the parliamentary contest, while the opposition pact led by the Democratic Action Party won the state of Penang. Koh remained visible in the political scene after the election, and even participated in a televised public debate with his successor as Chief Minister, Lim Guan Eng. He remained as Gerakan president, winning the post permanently in October 2008.
Cabinet minister
Koh returned to public office in April 2009, when he was appointed as a Senator in the Dewan Negara. This paved the way for prime minister Najib Tun Razak to name Koh in his inaugural Cabinet. He was appointed Minister in the Prime Minister's Department, in charge of unity and performance management. Koh was put in charge of Najib's Government Transformation Programme, which includes monitoring the performance of ministries and six national key result areas through Key Performance Indicators.
Stepping down as Penang BN leader
In August 2011, The Malaysian Insider reported that the central government of Putrajaya felt that Koh should step down as BN leader in Penang for the coalition to win back the state government in the 13th general elections. It was further said that voters viewed Koh as indecisive and a symbol of the BN leadership which was rejected by voters in 2008. Gerakan leaders reportedly encouraged Koh to leave Penang to contest the Simpang Renggam parliamentary seat, a Gerakan safe seat in Johor.
Resignation
On 16 May 2013, The Star reported that Koh officially resigned as the President of Gerakan. His deputy, Chang Ko Youn, would take over as acting president until the party elections on 26 October 2013. Koh's resignation followed Gerakan Secretary-General Teng Chang Yeow's earlier resignation as Penang Barisan Nasional chairman and Gerakan Secretary-General.
