In July 1961, the pro-communist faction in the People's Action Party (PAP) split from the non-communists to form Barisan Sosialis.
But Mr Jek Yeun Thong, a key member of the PAP Old Guard, stood firmly with the party's non-communist leadership.
He went on to help mobilise the Chinese-speaking ground to support the PAP's vision of a non-communist, multiracial Singapore.
"This was one of his biggest political contributions," Prime Minister Lee Hsien Loong said in a condolence letter to Mrs Jek Yeun Thong yesterday. It comes a day after Mr Jek's funeral on Tuesday.
Mr Jek, 87, died at home on Sunday, and in keeping with his wishes, his family held a private wake and funeral.
PM Lee, in his letter, paid tribute to Mr Jek, who served in Singapore's first Cabinet and was one of the 10 ministers who signed the Separation Agreement in 1965.
He was instrumental in building trust with the Chinese-speaking unions and helping the National Trades Union Congress wrest control of them from the Communist United Front.
PRIME MINISTER LEE HSIEN LOONG, in his tribute to Mr Jek Yeun Thong.
"Throughout his years in public service, Mr Jek made notable contributions, and demonstrated a strong sense of dedication to the nation," he said.
Mr Jek was Labour Minister and held other ministerial portfolios from 1963 to 1980. He remained an MP until 1988, and was conferred the Order of Nila Utama (Second Class) in 1990.
PM Lee recounted how Mr Jek came to know founding Prime Minister Lee Kuan Yew in the 1950s - a period when the Communist United Front dominated the labour and student unions, and the PAP had many communists in its ranks.
PM Lee noted that Mr Jek had left-wing sympathies and was arrested briefly in 1957, but came around to the non-communist side and was appointed political secretary to Mr Lee in 1959.
He was elected in the 1963 election, and made Labour Minister.
"He was instrumental in building trust with the Chinese-speaking unions and helping the National Trades Union Congress wrest control of them from the Communist United Front," PM Lee said.
He added that Mr Jek also helped draft and win support for the 1968 Employment Act - a key milestone in building harmonious labour relations which paved the way for Singapore to attract investments and industrialise in the 1970s.
In her condolence letter to Mrs Jek, President Halimah Yacob said that as Labour Minister from 1963 to 1968, Mr Jek had the foresight to build "the foundation in Singapore's foreign policy of seeking friends with all like-minded countries to facilitate our trade and industrial development".
President Halimah also recounted that Mr Jek spoke so passionately at the International Labour Organisation Conference in Geneva in 1966 that many in the audience began to take notice of the fledgling nation of Singapore.
In his seminal speech, Mr Jek had spoken about the importance of "setting a correct climate of labour relations", she said.
PM Lee said that as Minister for Culture from 1968 to 1979, Mr Jek raised the profile of cultural activities. "He believed that art transcended barriers of race, language and culture, and that traditional art could keep Singaporeans grounded at a time when the country was quickly modernising."
He also noted that as the People's Association deputy chairman, Mr Jek actively promoted photography competitions, art exhibitions and calligraphy contests - activities that strengthened grassroots communities.
"Mr Jek's passing is a deep loss to the nation," PM Lee said.