Foy Elisabeth Johnson was born in Riverton, Scotland County, on October 6, 1887, the second child and eldest daughter of Livingston Johnson and Mary Frances (Fannie) Memory. Livingston was a Baptist minister and editor of the Biblical Recorder.

Farmer was educated at public schools in Greensboro and Cary and received a bachelor of arts degree (1907) from the Baptist Female University, later Meredith College in Raleigh. Upon graduation, she taught high school for one year in Wake County before returning to her alma mater to teach in the preparatory department until 1911.

On June 7, 1911, Foy Johnson married Calder Truehart Willingham, a Georgia native and Southern Baptist Convention missionary. The two moved to Kokura, Japan, two months after their marriage, and once there, Foy began her evangelistic work, including teaching the Bible, English, and cooking. In summer 1918, the Willinghams left Yokohama, Japan for a furlough in the U.S. Unfortunately, while stateside, Calder Willingham was a casualty of the 1918 influenza pandemic, dying of influenza on October 15, 1918.

Farmer returned to her missionary work in Shimonoeskeki, Japan, but exhaustion and illness forced her permanent return to the U.S. in May 1921. She was married to James S. Farmer on January 19, 1922, in Wake County. James Farmer was manager and later editor of the Biblical Recorder, as her father had been.

Farmer held a lifelong commitment to Baptists. In addition to teaching Sunday school for many years, she was elected as a member-at-large of the Baptist State Convention's Women's Missionary Union (WMU), joining its executive board. She served the WMU in various capacities for roughly 50 years (1921-1971), including mission study chairwoman (3 years), prayer chairwoman (3 years), and vice president (5 years). She was president from 1942-1945 and again 1946-1950. She also served as vice president of the Southern Baptist Convention's WMU (1954-1960) and was on the Southern Baptist Convention's (SBC) Foreign Mission Board (1943-1963). Nor was she bound solely to the U.S.; Farmer was a member of the board of directors for the University of Shanghai and maintained relationships with numerous missionaries around the world. Foy was also a trustee of Shaw University (1946-1953) and Meredith College (1933-1963). Foy also found the time throughout her busy life to author a number of books, including At the Gate of Asia,  Publishing Glad Tidings,  Mrs. Maynard's House,  Sallie Bailey Jones,  Hitherto: History of North Carolina's Woman's Missionary Union,  The King's Way, and  Sacrifice and Song.

Foy Elisabeth Willingham Farmer had two children who lived to adulthood with James Farmer: daughter Fannie J. M. Farmer and son James Stephen Farmer. She died May 29, 1971, and is buried at Oakwood Cemetery in Raleigh.