S. Rajaratnam was born in 1915 in Jaffna, Ceylon (now Sri Lanka) and was raised in Seremban, Malaysia, where his father rose from being a supervisor of rubber estates to a plantation owner. He attended the Convent of the Holy Infant Jesus for six months and was transferred to St Paul's, a boys' school. He continued his education in the prestigious Victoria Institution in Kuala Lumpur and then in Raffles Institution, Singapore.
In 1937, He went to King's College, London, to pursue a law degree. There he received his political awakening, became fashionably anti-imperial, anti-British, joined the socialist Left Book Club and became a Marxist.
The lack of communication between London and Malaya during the Second World War meant that Rajaratnam could no longer receive money from his father to continue his education. He therefore turned to journalism to earn a living, never returning to university to complete his degree.
On his return to Singapore in 1948, he joined the Malayan Tribune. In 1950, he was appointed Associate Editor of the Singapore Standard and held that post for four years. He then worked for The Straits Times till 1959. He was the secretary of the Malayan Indian Congress and a founder member of the Singapore Union of Journalists. His writing was clearly of the Left and anti-British, but at the same time he was not for the Communists.
Rajaratnam met Lee Kuan Yew by chance at the Chinese Swimming Club. Recognising that they were both dissatisfied with the prevailing political situation, they arranged to meet to discuss the situation. Rajaratnam became a founding member of the People's Action Party. In 1959, he resigned from The Straits Times to run for the Legislative Assembly seat of Kampong Glam.
S. Rajaratnam is recognised and recognises himself as the theoretician and ideologue of the People's Action Party. In his own words, "the ideas man," "a public relations man… who projects the PAP image."
He is also known as a strong believer in multi-racial Singapore. In 1966, with the 1964 race riots fresh in his mind, he wrote the National Pledge containing the words, "One united people, regardless of race, language or religion."
He also wrote 'PAP's first ten years', published in the 1964 souvenir publication marking the party's tenth anniversary. This account, the first by a minister and founding party member, has become a classic reference for subsequent accounts of Singapore's history of independence.
In Cabinet, Rajaratnam served as Minister for Culture (1959), Minister for Foreign Affairs (1965), Minister of Labour (1968-71) and second Deputy Prime Minister (1973). He was appointed Senior Minister in 1988 after he retired from active politics.