He led the civilian wing of Khana Ratsadon, and helped found the University of Moral and Political Sciences and the Bank of Thailand.

Born to a family of farmers in Ayutthaya province, he received a good education, becoming one of the nation's youngest barristers in 1919, at the age of nineteen.

In the aftermath of 1932 Siamese Revolution, he played an important role in drafting two of the country's first constitutions and proposing a socialist economic plan influenced by communism scheme, principles and conducts.

His contributions include modernizing Thai legal codes, laying the foundation for Thailand's local government system, negotiating the cancellation of unequal treaties with the West, and tax reform.

Pridi diverged from Plaek Phibunsongkhram after the latter began to display a taste for dictatorial governance in the 1930s, marking the beginning of the long rivalry between the two Khana Ratsadon leaders.

[6] Pridi wrote that his great-great-great-grandfather, Heng, was a native of Etang Village in the Chenghai County of Guangdong Province, southern China, who came to Siam during the reign of Boromaracha V (Ekkathat) (r. 1758–1767), leaving behind his wife, who was pregnant with their son, Seng.

When Nai Koet died, his wife directed that his remains were to be cremated and interred at the shrine at Phanomyong Hill, which is the origin of their Thai surname.

[10] On 24 June 1932, Khana Ratsadon, the tiny People's Party, with Pridi as the leader of the civilian faction, carried out a lightning coup that abruptly ended 150 years of absolute monarchy under the Chakri dynasty.

[13] Although he had been friends with Field Marshal Plaek Phibunsongkhram during the early days of the People's Party, the two fell out in subsequent years.

On 8 December 1941, Imperial Japan launched attacks on Southeast Asia and the Allied possessions in the region, opening the Pacific War.

After initially resisting, the Thai government reluctantly agreed to let the Japanese pass through the country and use its military bases to strike other Allied possessions in the region, culminating in the Battle of Malaya.

When Field Marshal Plaek Phibunsongkhram issued a declaration of war against Britain and the United States in January 1942, Pridi refused to sign it, as he served as the Regent for the young monarch, who was studying in Switzerland.

Code named "Ruth", he established contact with the Allies and Thai resistance organisations in Britain and the United States.

As the war progressed and the fortunes of the Japanese declined, public dissatisfaction grew and Phibun was forced to resign as prime minister in 1944.

When Japan's surrender ended the war, the Seri Thai-dominated government immediately acted to "restore the pre-war status quo".

He was formally named a Senior Statesman (Ratthaburut Awuso), and served as an advisor to the post-war, civilian governments of Thawi Bunyaket and Seni Pramoj.

Sulak Sivaraksa, a prominent conservative and monarchist, wrote that Pridi's role in the event was he protected responsible royals, and prevented the arrest of a person[15] who destroyed the evidence.

[17] After a general election, Pridi resigned as prime minister, resumed his role of senior statesman, and left on a world tour, visiting Generalissimo Chiang Kai-shek and US president Harry S. Truman along the way.

The coup, led by Lieutenant General Phin Choonhavan and Colonel Kat Katsongkhram, ousted Thamrong's government, which is the political ally of Pridi.

Rumours were spread that Pridi was part of a conspiracy involved in the alleged regicide, and that he had plans to turn Thailand into a republic.

In his later years, Seni Pramoj promoted the idea that he had saved Thailand from post-war British colonial rule that Pridi had been willing to accept.

[20] Nigel Brailey treats the Free Thai movement as largely a sham and casts doubt on Pridi's part, arguing "it appears questionable whether Pridi committed himself personally to the Allied cause much prior to August 1942, if even then," suggesting that "his eventual anti-Japanese stance was a consequence primarily of his hostility to Phibun.

However, Pridi recognised well before the war that Thailand's alignment with the Axis powers would work to Phibun's advantage and enable him to strengthen his dictatorship.

On 30 October 1999, UNESCO included the centenary of Pridi Phanomyong's birth in its recognition of anniversaries of great personalities and historic events as tribute to his ideals and integrity.