Phomvihane attended law school at Hanoi University in Hanoi, Vietnam. He dropped out of law school to fight the French colonialists who were in Vietnam. Later, he joined the Pathet Lao, which was also fighting the French colonialists.
He died in Vientiane, Laos. After his death, the Laotian government built an eight million dollar gold-plated museum in his honor, in Vientiane, partially funded by Vietnam, with a 30 foot, cast-iron, statue of Phomvihane as a middle-aged pot-bellied gentleman in a tight-fitting suit in front of the building.
He became an active revolutionary while studying in the Indochinese capital of Hanoi during the 1940s. In 1955 he was instrumental in setting up the LPRP at Samnuea in northern Laos, and subsequently served as the Pathet Lao leader, although Souphanouvong served as the figurehead. In the years which followed he led communist forces against the Kingdom of Laos and the Americans. After their victory he served as Prime Minister from the founding of the Lao PDR in 1972 until 1991. He married to Thongvinh Phomvihane, an ethnic Vietnamese. They were childless, but had adopted a son. After his death, the Lao communist party relieved his wife of her party membership, over allegations of heroin trafficking, apparently using her diplomatic status to transport heroin into Vietnam several times.
Phomvihane displayed expert skills in handling relations with Vietnam. On occasions there were disagreements over Lao-Viet border issues. Lao and Vietnamese forces almost clashed over their common border. The Lao communist party chose the tactic of ignoring and delaying over Lao/Viet border issues. The demarcation process started in 1977 and just finished in 2007. According to western journalist the Lao/Viet borderline is "very close" to the 1945 border between Laos and Tonkin and Annam, respectively.
According to Vatthana Pholsena, Assistant professor of Southeast Asian Studies at the National University of Singapore, the author of the book "Post-war Laos" Kaysone Phomvihane was the top policy maker in LPDR, and a strongman. He created Sekong province to honor the southern minority for their support on the war effort.