Shigeyo Nakachi was born as Shigeyo Hiraishi in Saga, Japan on 1 February 1905, as the second of seven siblings. Her mother was Kayo Hiraishi. In 1911, she entered elementary school. In 1913, she received an award for excellence. In 1916, she graduated from elementary school.
In 1923, she became a teacher. In 1929, at the age of 24, she married Goro Nakachi. The couple had one son: Kenzo. After the end of the World War II, she began teaching at an elementary school dedicated to those returning from Manchuria.
She became a kindergarten teacher when she was age 46. Her husband died in 1961. She retired from a kindergarten teacher in 1967 at the age of 62.
Nakachi suffered from breast cancer at the age of 80 and underwent surgery to remove one of her breasts. After retiring, Nakachi enjoyed traveling around Japan with her ex-students and her hobby tea ceremony friends until the age of 92.
She fell in the bus at the age of 92 and broke her femur. She then broke her opposite femur at the age of 93 and around her buttocks at the age of 101, but until the age of 106 she lived with her family at home. At the age of 108, she could walk unassisted. Nakachi enjoyed hand-dancing. She was almost completely deaf. In February 2014, December 2018, and April 2019, she recovered from a bout of aspiration pneumonia that left her bedridden and requiring a breathing tube for several days.
Nakachi died in Saga City, Saga Prefecture, Japan, on 11 January 2021 at the age of 115 years, 345 days.
Nakachi had been the oldest living person in Saga Prefecture from the death of 112-year old Nugi Ikeda on 8 June 2016 until her death. Following the death of Shin Matsushita on 27 August 2019, she became the second-oldest living person in Japan (behind Kane Tanaka) and the fifth-oldest validated living person in the world.
On 14 February 2020, Nakachi became the oldest person ever documented from Saga Prefecture after breaking the previous record of 115 years, 12 days set by Chiyono Hasegawa. After surpassing the final age of Shimoe Akiyama on 14 October 2020, Nakachi became the seventh-oldest validated person in Japanese history.
At the time of her death, Nakachi was the 24th-oldest person of all-time whose age has been validated by the GRG.