Sim had been the DAP state chairman for Malacca until succeeded by Goh Leong San after a hotly contested internal state election on 19 December 2005, which also saw DAP secretary-general Lim Guan Eng and his wife Betty Chew get the lowest number of votes out of 15 candidates, thus causing Chew to lose her seat on the Malacca DAP committee entirely. On 20 April 2013, the nomination day of the 2013 general election, beside registering as DAP official candidate to defend his Kota Melaka parliamentary seat, Sim made a surprise commotion registering to contest the Kota Laksamana state seat too but as an Independent against DAP candidate concurrently causing DAP to expel him. But only two days later on 22 April he announced his withdrawal as the state seat of Kota Laksamana Independent candidate to fully back the DAP candidate, Lai Keun Ban, instead and to focus to continue defend the Kota Melaka parliamentary seat under the DAP. As preparation for the voting day on 5 May already done by the Election Commission of Malaysia, thus his candidacy still appeared on the ballots and managed to get 1,242 that finish last among three candidates but still lost his deposit in the election. On 17 September 2015, a doctor from Malacca who is also the Bukit Palah DAP branch chairman, Dr Wong Fort Pin, successfully sued Sim and Goh for defamation and won RM300,000 in damages. Both Sim and Goh party membership was suspended for one-year suspension on 16 February 2016, reportedly for disparaging the party. On 12 February 2017, Sim, along with three other DAP Malacca state assemblymennamely Goh, Lim Jack Wong, and Chin Choong Seong announced their resignation from the party to be Independent, citing lack of trust in DAP leadership. They formed the 'Justice League' to contest in the 2018 general election as independent candidates using the key as their common symbol. Sim will be contesting the Kota Laksamana state seat whereas Goh will go for both parliamentary and state seat. Lim and Chin will contest the Ayer Keroh and Bandar Hilir state seats respectively. In the 2018 general election, Sim contested the state seat of Kota Laksamana as independent candidate but lost.
Election results
Sim who surprisingly registered as an Independent candidate but announced his withdrawal two days after nomination to support DAP candidate Lai Keun Ban, somehow still had his candidacy officially appeared on the ballot on voting day.