After the Kon-Tiki expedition, Danielsson married in Lima a French woman, Marie-Thérèse (1923–2003), and they decided to settle in Raroia, the atoll on which the raft had made landfall. They stayed there from 1949 to 1952, and in 1953 they moved to Tahiti. His doctoral thesis on the Tuamotus island chain, submitted to Uppsala University in 1955, was published the following year as Work and Life on Raroia. He subsequently wrote many books and scripted many films, becoming one of the world's foremost students of Polynesia. He and his wife were particularly outspoken critics of French nuclear tests at Moruroa and Fangataufa atolls, and of the destruction of Polynesian culture through colonialism. Their daughter Maruia (1952–1972) died from cancer.
Danielsson received the Right Livelihood Award for his campaigning work in 1991. He died in July 1997 following a deterioration in his health, and was buried in Mjölby, Sweden.