A colourful and stirring orator, Marshall led the left-wing Labour Front to a narrow victory in Singapore's first Legislative Assembly elections in April 1955. He formed a minority government and become Chief Minister. He presided over a shaky government, receiving little co-operation from either the colonial authorities or the other local parties. In May 1955, the Hock Lee Bus Riots broke out, killing 4 people.
In April 1956 he led a delegation to London to negotiate for complete self-rule, but the talks broke down over British concerns about worker unrest and communist influence. After the failed meeting, Marshall resigned saying "I have failed in my Merdeka mission". Replacing him as Chief Minister was Lim Yew Hock, who would later take very tough action against the labour unions. However, Lim Yew Hock, like the subsequent PAP government, also built on many of Marshall's other ideas and reforms.
After resigning, Marshall visited China for two months, at the invitation of Premier Zhou Enlai. Contacted by a representative of a group of over 400 Russian Jews who were being refused exit from Shanghai by the Chinese authorities, Marshall intervened with the Premier and managed to have them released.[1]
After returning to Singapore, Marshall stayed on the backbenches before quitting the ruling Labour Front party and as a member of parliament in 1957 and founding the Workers' Party of Singapore. He lost his old seat of Cairnhill to incumbent chief minister Lim Yew Hock in the 1959 general election on the WP ticket, but won a by-election in Anson in 1961. After losing his seat again in the 1963 elections contesting as an independent, he returned to practise law and remained active in opposition politics even after J. B. Jeyaretnam became leader of the Workers' Party in 1972.
From 1978 to 1993, Marshall served as Singapore's Ambassador to France, Portugal, Spain and Switzerland. As ambassador, Marshall always defended his country's interests, despite his differences with Lee Kuan Yew's government. He retired from the diplomatic corps in 1993.