The main objectives of the Barisan included eradicating colonialism, establishing a united independent and democratic Malayan nation comprising the Federation of Malaya and Singapore and introducing an economic system to promote prosperity and stability in society.

[2] With the support of the working class, the PAP won the third-most seats in the 1955 election and formed the main opposition.

The merger with Malaysia was supported by the Lee Kuan Yew camp as a means of assuring Singapore's future security and prosperity, while opposed by the left-wing camp as the merger was seen as an attempt to "wipe out the left-wing forces in Singapore" (Interview with Dr Lee Siew Choh).

At the meeting, the left got assurance from Selkirk that Britain was committed to independence and would not intervene militarily to maintain control after the overthrow of Lee Kuan Yew's government.

[6][7] On 20 July 1961, Lee Kuan Yew called an emergency meeting of the Legislative Assembly to vote on a motion of confidence in the Government.

The expelled members, including Lim Chin Siong, Sidney Woodhull and Fong Swee Suan, then proceeded to form an opposition party, the Barisan Sosialis.

[5][8] The Barisan was officially inaugurated on 17 September 1962, with Lim Chin Siong as its secretary-general and Dr Lee Siew Choh as chairman.

The Referendum Bill on the merger incorporated proposals and amendments from the Barisan, David Marshall, Ong Eng Guan and SPA-UMNO.

[5] This move had been anticipated by the PAP government; a clause had been inserted within the Referendum Ordinance stating that voters who cast blank votes were unable to make a decision themselves and they must necessarily follow the majority.

[6] The Barisan's open support of the Brunei revolt gave the PAP an excuse that the arrests were to prevent possible communist subversion and safeguard the security and safety in Singapore.

Under the action, code-named Operation Coldstore, 107 people including political, trade unionists and student leaders who had shown support for the Brunei Revolt were detained.

Operation Coldstore almost paralysed the Barisan because of the detention of its major leaders including Lim Chin Siong.

On 22 April 1963, Lee Siew Choh and remaining Barisan activists launched the "City Hall Battle".

[5] After Operation Coldstore and ensuing protests, major cadres of Barisan were detained or put on long trials.

The Barisan won thirteen, and the remaining seat fell to Ong Eng Guan who contested under the banner of the United People's Party.

[5] Soon after Malaysia was formed, alarmed by Indonesia's confrontation and rebel activities in the Borneo territories, the central parliament in Kuala Lumpur passed legislation which required all youth between the age of 18 and 25 to register for National Service.

[4] The left-wingers regarded this action as a government move "to counter the left-wing movement"[5] However, within the left-wing camp, there were two different strategies to campaign against the National Service scheme supported by two schools led respectively by Chen Hock Wah, who was a member of the CPM and Lee Siew Choh, who was Chairman of Barisan.

On the other hand, the camp led by Lee Siew Choh advocated a boycott of the law and proposed affected persons should not even register in the first place.

Taking the view that there was neither true national independence nor parliamentary democracy, Barisan began to boycott Parliament and elections.

[9] In October 1966, the Barisan had all its remaining representatives in Parliament resign their seats and started what they called an extra-parliamentary struggle.