The Southeast Asian Games owes its origins to the South East Asian Peninsula Games or SEAP Games. On 22 May 1958, delegates from the countries in Southeast Asian Peninsula attending the Asian Games in Tokyo, Japan had a meeting and agreed to establish a sport organisation. The SEAP Games was conceptualised by Luang Sukhum Nayaoradit, then Vice-President of the Thailand Olympic Committee. The proposed rationale was that a regional sports event will help promote co-operation, understanding and relations among countries in the Southeast Asian region.

Six countries, Burma (now Myanmar), Kampuchea (now Cambodia), Laos, Malaya (now Malaysia), Thailand and Vietnam were the founding members. These countries agreed to hold the Games biennially in June 1959 and SEAP Games Federation Committee was formed thereafter.

The first SEAP Games were held in Bangkok from 12–17 December 1959 comprising more than 527 athletes and officials from Thailand, Burma, Malaya (now Malaysia), Singapore, South Vietnam and Laos participating in 12 sports.

According to wikipedia