While Malaya was still under the control of the British, businessman Tun (Sir) Tan Cheng Lock founded an organization designed to represent Malaya's Chinese population, the Malayan Chinese Association. Drawn to their goals, Sim joined the MCA in 1949, in their earliest days.
殖民時代，祖籍漳州、學通中西的殷商陳禎祿爵士發起組織代表華人的政黨「馬華公會」，沈慕羽受其感召，1949 年成立之初就已加入。