Born in Musashino, Tokyo, Japan. Her father was a Sankei Shimbun newspaper reporter. She spent her childhood in Fukui city, where her wealthy family ran the geisha ryokan Beniya at Awara Onsen. Later her father was defeated in the general election, and, heavily in debt, the Yamatani family left Fukui for Tokyo. She attended the University of the Sacred Heart and worked in the United States for a publishing company. She became the editor-in-chief of Sankei Living Shimbun in 1985 and became known as an essayist and television personality.
In June 2000, she was elected to the Diet of Japan on the Democratic Party of Japan ticket as a proportional representative. She left the party in 2002 to join the New Conservative Party. Though she had planned to run for the seat representing the Tokyo 3rd district in 2003, the emergence of Hirotaka Ishihara, son of Governor Shintaro Ishihara, forced her to run from the 4th district, where she was defeated. She then returned to the Diet as a proportional representative of the Liberal Democratic Party in 2004.
Yamatani is a vocal opponent of "gender-free education" and of sex education in home economics textbooks and other parts of the school curriculum. She is also a supporter of Japan's territorial claims and has called for special legislation to restrict land sales to foreigners on Tsushima Island and to implement measures to boost its local economy without having to depend heavily on South Korean tourists. Koreans own about 0.007 percent of the land on Tsushima.
- The Japan Times Kumagai to form 'new party' with NCP and DPJ defectors December 25 2002 Retrieved on August 7 2012
- Kaneko, Maya, (Kyodo News) "Tsushima's S. Koreans: guests or guerrillas?", Japan Times, March 5, 2010, p. 3.
- "Eriko Yamatani's Lecture on June 14, 2005 at Mitaka Marketing Plaza"  reported by CGS, International Christian University