Underwood was born as Eliza Jane Brown in Clinton, North Carolina on 15 March 1867 as the fifth of nine children born to Charles and Violet (née Butler) Brown, both former slaves. At the age of eight, she went to live with the Royals, a white family who lived nearby, later returning to live with her own family aged 15.
In 1890, she married preacher Isham Underwood, and their only daughter, Lenorah, was born in September of that year. The family later moved to Taylor, Georgia, and lived there until they adopted a baby girl, Minnie, in 1912. They lived in Hancock and Jefferson Davis, both in Mississippi, before settling in Columbia, Mississippi, and staying there for several decades. She weaved cloth and worked in fields.
Underwood was widowed in 1953 and moved to San Antonio, Texas in 1973 to live with her daughter, Lenorah Grant. Four years prior, she had flown on a plane from Columbia to San Antonio to visit her daughter, enjoying the trip immensely. In her younger years, she also traveled to Canada and Mexico.
In 1979, her daughter died, and Underwood went to live with her adopted daughter, Minnie Simmons, in Washington D.C.
Underwood claimed that the secret to her longevity was never smoking or drinking alcohol, and being active in church-related activities. As a supercentenarian, she had seven grandchildren, 18 great-grandchildren, and 10 great-great-grandchildren.
Starting from 1973, Underwood was reported regularly on her birthday in various San Antonio newspapers. She was honoured by the American Freedom Train during the U. S.’s bicentennial celebrations in 1976.
Her age was verified by Jimmy Lindberg and Nick Eriksson, and validated by LongeviQuest on 9 October 2023. After her age was verified and it was established that she lived to be at least 113 years and 318 days, it was concluded that she held several titles and set several records during her life. These are as follows:
On 5 November 1978, following the death of 113-year-old Alice Coles, she became the world’s oldest living person, at the age of 111 years, 235 days. Prior to her validation, it was believed that, at the time of her passing, Augustine Tessier held the title of the oldest living person, with the previous title holder being Fannie Thomas, who had passed away just five days prior to Underwood. However, Underwood was at least a month older than Thomas, and nearly two years older that Tessier.
On 16 October 1979, she reached the age of 113 years, 215 days, surpassing the final age of Delina Filkins (1815–1928) – the oldest validated person on record of the time. Prior to Underwood’s validation, it was thought that Filkins was succeeded as the oldest person ever by Fannie Thomas in November 1980. However, Underwood’s birth appears to have occurred before Thomas’, regardless of the specific birthdate (details below). Furthermore, Thomas passed away at the age of 113 years and 283 days, which means that, although she outlived Underwood, she never surpassed her final age.
* “Worlds of wisdom at 109 years old” – San Antonio Express, 3 February 1977
* “110 – Mrs. Eliza Underwood of San Antonio, Texas” – Columbian-Progress, 9 June 1977
* The Washington Star, 30 January 1981