She made her political debut in the 2011 general election as part of a four-member PAP team contesting in Holland–Bukit Timah GRC, and won 60.1% of the vote.

From 2007 to 2009, Sim was seconded to the International Enterprise Singapore as its Regional Director based in Shanghai, where she headed a team assisting Singapore-based companies with investment and sales in East China.

Sim entered politics when she joined a four-member People's Action Party team to contest in Holland–Bukit Timah GRC during the 2011 general election.

[2] During the 2015 general election, Sim contested as part of a four-member PAP team in Holland–Bukit Timah GRC again and they won with 66.6% of the vote against the Singapore Democratic Party.

[5][2] At the 2020 general election, Sim joined the four-member PAP team contesting in Holland–Bukit Timah GRC again and they won with 66.36% of the vote against the Singapore Democratic Party.

[2] Sim is married to Mok Ying Jang, a doctor who is the Deputy Chief Operating Officer of the National Healthcare Group Polyclinics.