The agreement included a Proclamation on Singapore to be made by Malaysian Prime Minister Tunku Abdul Rahman; a different Proclamation of Singapore was made by Singaporean Prime Minister Lee Kuan Yew.

From 1959 to 1963, Singapore was a country with full internal self-governance, but the British colonial administration still controlled external relations, similar to the Irish Free State.

On 16 September 1963, the Proclamation of Malaysia was declared, which declared the merger of four countries: Malaya, North Borneo (Sabah), Sarawak and Singapore – the latter three already self-governing colonies by this point – into the new entity of Malaysia.

With this, Singapore subsequently joined Malaysia as an autonomous state, along with Sarawak and Sabah.

The short-lived union would prove tenuous due to various factors, including deep political and economic differences, and would end up lasting for just 1 year, 10 months and 24 days before this agreement became effective on 9 August 1965.