Living as a young traveller in Europe, Asia and Australia during the 1980s and 1990s he became involved in many civil and human rights campaign activities. He travelled widely as a painter, writer, filmmaker and human rights activist before he returned to Malaysia from Australia during the mid 90s, and practices laws at Cheah Kah Peng & Co., Penang.[4]
The political party he helped to construct focused on dismantling its colonial legacy of racial divide (or apartheid) through tackling institutionalised racism, poverty and inequality. He was elected as member of the party's Supreme Council and served as central committee member from 1999 to 2010. He was reported to be one of the International Human Rights lawyers at risk in international journals from 1999 to 2003 during which he was one of the few lawyers who stood up against Malaysia's draconian Internal Security Act (ISA).[5] In the year 2000, he was arrested and imprisoned in Malaysia for a trumped up charge of obstructing police officers in execution of their duty while the truth was that he tried to stop the police from causing grievous bodily harm to political detainees.[6]
In the 2013 general election, he was picked by PKR to contest and won the Penang state seat of Kebun Bunga to be its assemblyman.
In 2017, Cheah was excluded from the PH assemblypersons list, who were to register victims of the Penang's devastating floods on 4–5 November in their own constituency for the state's initiated post-flood relief aid of RM700 for every eligible recipient. The Chief Minister Lim announced he together with the Pulau Tikus assemblyperson Yap Soo Huey instead would register floods victims in Cheah's Kebun Bunga constituency, near Botanical Gardens.[11] To counter back, a defiant Cheah held a similar programme not far away from the one organised by the state government.[12]
As speculated, Cheah was dropped by PKR as the PH candidate,[13] to make way of the Kebun Bunga seat for the predecessor assemblyman, Jason Ong Khan Lee returning to contest the 2018 general election.[14] Ong managed to win the election on 9 May 2018 to be the Kebun Bunga assemblyman again.[15]