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.[3]
However he was chosen by DAP to contest the Kota Melaka parliamentary seat in the 2008 general election but he won by beating predecessor Wong Nai Chee of Malaysian Chinese Association (MCA) with a majority 11,390 vote and retained it again in the 2013 general election by beating Yee Kok Wah of MCA with a majority 20,746 vote. But on the 20 April nomination day of the election, beside registering as DAP official candidate to defend his Kota Melaka parliamentary seat, Sim made a surprise commotion by also registering to contest the Kota Laksamana state seat too but as an Independent against DAP candidate concurrently, causing DAP to initially expel him.[4] 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.[5] As preparation for the voting day on 5 May already done by the Election Commission (EC),[6] thus his candidacy still appeared on the ballots and managed to get 1,242 votes that finish last among three candidates and still had his deposit forfeited in the election.[7]
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.[8] Both Sim and Goh party membership was suspended for one-year suspension on 16 February 2016, reportedly for disparaging the party.[9]
On 12 February 2017, Sim, along with three other DAP Malacca state assemblymen namely Goh (Duyong), Lim Jack Wong (Bachang) and Chin Choong Seong (Kesidang) announced their resignation from the party to be Independent, citing lack of trust in DAP leadership.[10] They formed the 'Justice League' to contest in the 2018 general election (GE14) as independent candidates using the key as their common symbol.[11] Sim contested the Kota Laksamana state seat whereas Goh will go for both parliamentary (Kota Malacca) and state seat (Kesidang). Lim and Chin will contest the Ayer Keroh and Bandar Hilir state seats respectively.[12] In the GE14, Sim officially contested first time as independent candidate for the state seat of Kota Laksamana but lost.[13]
A Sim who surprisingly registered as an Independent candidate on nomination day but withdrew later to support DAP named candidate, still had his candidacy appeared on the EC voting ballot officially. B Sim and three others MLA who had quit DAP Malacca earlier, had formed the 'Justice League' informal Independent bloc and contested as Independent candidates using the key symbol.
