Harold Louis Day was born March 16, 1913, to Thomas and Mabel Day in Standard, IL, where his father was a laborer. The Day family included Harold's brother, Wilbur, and two sisters, Esther and Ruth. Harold attended elementary school at Standard School between 1920 and 1928. His parents made a decision to move to Chicago in search of better job opportunities, and Harold attended Lane Technical High School in Chicago between 1930 and 1932.

After graduation, Day began working in valve and chrome plating plants, and was employed at Vacuum Can Company betwen 1938 and 1942. Because of health problems, he transferred to plating work at Glenview Naval Air Station, and then worked briefly as a janitorial assistant at the Chicago Gospel Tabernacle.

He was married on June 29, 1940, to Dorothea Finney, and they had three children: Roger, Thomas, and Juanita born between 1942 and 1946. Day began employment in 1946 as an engineering maintenance man for the American College of Surgeons, and continued in this capacity until his retirement in 1979.

Day's sister Ruth worked as a secretary at Chicago Gospel Tabernacle, then under the leadership of Paul Rader. At his sister's urging he began attending services, and subsequently was baptized by Rader. Day remained active in the work of the Tabernacle in a volunteer capacity, and continued in this work until 1978.

Day and his wife lived in Wheaton, Illinois. He died September 30, 2006.