In 1946, Phetsarath became leader of the Lao resistance movement against the French return to Laos, a position which placed him in direct conflict with the King, who sought a return to the French Protectorate. Consequently, Phetsarath left the country and spent eleven years in exile in Thailand, a period during which Lao politics was dominated by his younger brothers, the Princes Souvanna Phouma and Souphanouvong.

Phetsarath finally returned to Laos in 1956 to act as mediator in the conflict between Souvanna Phouma and Souphanouvong and died in his birthplace Luang Prabang in 1959.

The rivalries between the three brothers mirror the plight of modern Laos.
In his memoirs, Phetsarath is critical of Souvanna Phouma for being too willing to along with the French and too willing to settle for half measures on the road to full independence. Prince Phetsarath offers great praise to Souphanouvong as a fighter for freedom and national liberation but criticizes him for becoming drawn too close to the Vietnamese. Similarly, he criticizes Souvanna Phouma for having a French wife and Souphanouvong for marrying a Vietnamese woman. At the same time Phetsarath had strong affinities for Thailand, as well as his marriage to a Thai.
These three brothers, both in their politics and in their choices of wives, represent the three chief divisive tendencies in Lao politics of the period. Orientations toward France, Vietnam and Thailand.

To many Lao people Prince Phetsarath represented both continuity with the pre colonial past and the hope of a new, post colonial future, he was both a traditionalist, by culture and by his affinity with the Lao (people among whom he was so popular), and a modernist, determined to forge a new Lao unity where a history of kingdoms and principalities had existed before. He was both an aristocrat, a member of a powerful viceregal family, and a democrat. His life is indelibly imprinted into the modern history of Laos.