Agnes Sligh was born to a Scottish immigrant father and a mother who was a native of the Scottish community of Westmoreland County, Pennsylvania. This background would contribute to the vocabulary Agnes used in many of her novels. She attended the village school as a child then went away to boarding school because there was no local high school. Later she attended Indiana State Teachers College (now Indiana University of Pennsylvania), graduating Phi Beta Kappa. In 1918, the same year she began teaching high school English, Agnes married James Lyall Turnbull, who left to fight in World War I a month after their wedding. He survived the war and they were married for 40 years, with one daughter. At the end of the war, Agnes Sligh Turnbull sold her first short story to The American Magazine. She achieved success as a short story writer before deciding to write novels. Her first published novel was The Rolling Years (1936), a story of three generations of Scots in Westmoreland County and their struggles to maintain their strict Presbyterian faith in a secular world. Many of her other "Pennsylvania" novels dealt with similar themes. She also wrote four juvenile novels, including Elijah the Fish-bite (1940) and The White Lark (1968). Her early diaries were excerpted in Dear Me: Leaves from the Diary of Agnes Sligh Turnbull (1941). Although her books are mostly forgotten today, in their time they sold millions of copies and got favorable reviews.