After finishing his military career with the rank of air chief marshal, he served as the foreign minister of Thailand from 1980 to 1990.

[5] Two of Siddhis sisters married US intelligence operatives, one was the wife of former OSS agent Willis Bird and one of CIA officer William Lair.

As Thailand' representative in the United Nations (UN) and ASEAN, Siddhi advocated a tough line towards Vietnam which was occupying Cambodia after 1979.

In 1983, Siddhi was elected member of parliament and in 1985 he took over the leadership of the Social Action Party (SAP) following the retirement of Kukrit Pramoj.

In August 1990, the new Prime Minister Chatichai Choonhavan dismissed Siddhi as he sought a more pragmatic relationship with the communist-ruled countries of Southeast Asia.

[8] On 8 May 2000, he was among the five Free Thai veterans who were awarded the Agency Seal Medallion by CIA director George Tenet.