Through the 1950s and 1960s, he worked with the Central Intelligence Agency of the United States during its unsuccessful campaign to use armed Tibetan rebels against China.

[2][2] After US support of the Tibetan resistance ended in the 1970s, he often acted as the Dalai Lama's unofficial envoy to China and attempted to negotiate his return.

Following his death at age 96, The Washington Post said Thondup was "arguably the second-most important figure in modern Tibetan history", viewed by many governments around the world as a de facto political leader of Tibet.

[1] Fluent in Chinese, Tibetan and English,[8] in subsequent decades, Thondup traveled between New Delhi, Taipei, Washington, Hong Kong, and Beijing as an unofficial envoy.

[1] In the late 1950s and early 1960s, the CIA provided the resistance with an estimated 700,000 pounds of rifles, ammunition, grenades, and radio equipment, and airdropped them into Tibet, but their missions were unsuccessful.

[1] In 1959, Thondup helped to orchestrate the Dalai Lama's safe passage to India after his escape from Tibet, where he was being held by Chinese authorities.

[1] With the permission of the Dalai Lama, Thondup met Chinese leader Deng Xiaoping in 1979 for peaceful political talks, to negotiate terms for his brother's return to Tibet.

[14] In recent years, Thondup urged Tibetans to remain politically engaged, repeatedly stating that dialogue was the only way to achieve progress with China.