In 1956 Sim was appointed a justice of the peace by the British colonial government. During the push for independence, Sim again set to work with the MCA, working alongside Malays and Indians in an effort to establish their own nation.
1956 年，沈慕羽被殖民政府英國女皇賜封為「太平局紳」；馬來亞獨立運動期間，沈慕羽又跟隨馬華公會會長陳禎祿奔走呼號，與馬來人、印度人並肩打拚，爭取建國，許多群眾大會及宣傳文告多出自沈慕羽手筆。