Junichiro Koizumi was born on 8 January 1942 in Yokosuka, Kanagawa Prefecture. He was one of six children born to mother Yoshi and father Junya Koizumi. Prime Minister Koizumi's father and grandfather both served in Japanese government. His grandfather, Matahiro Koizumi, a farmer's son, was a plasterer before becoming a member of the House of Representatives (the lower house of Parliament) and eventually a cabinet member before World War II (1939–45). Koizumi's father married Matahiro's daughter Yoshi. He also ran for Parliament and even served there at the same time as his father-in-law.
Junichiro Koizumi graduated with a degree in economics from the Keio University Faculty of Economics in 1967. He then went on for postgraduate work at the London School of Economics, and left to return to Japan on the death of his father. He ran unsuccessfully for his father's seat in Parliament, but became a junior secretary to Takeo Fukuda, Member of the House of Representatives who later became prime minister. Gaining experience under Fukuda's influence, Koizumi himself was elected a Member of House of Representatives in 1972. He subsequently served 10 consecutive terms.
Koizumi married Kayoko Miyamoto, granddaughter of the founder of one of Japan's major pharmaceutical companies. The couple had two sons before divorcing. Koizumi remains single, a rare situation for a high-ranking Japanese politician. Considered a colorful character, gossip surrounds his social activities. Koizumi himself claims to love pop music and karaoke, and he says his favorite leisure activity is listening to opera at home.