Thomas Edgar Lyon Sr., eighth child and seventh son of David Ross Lyon and Mary Cairns, was born in Salt Lake City, Utah, on August 9, 1903. He was educated in Salt Lake City public schools and attended LDS High School; he earned degrees from the University of Utah (B.A. 1927; Ph.D. 1962) and the University of Chicago (M.A., 1932). He married Hermana Forsberg in the Salt Lake Temple on August 16, 1927; they became the parents of six sons, including two sets of twins. A member of the Church of Jesus Christ of Latter-day Saints, he was called as president of the Netherlands Mission, where he had been a missionary from 1923-1925, serving in that capacity from 1933-1937. Upon the family's return from the Netherlands, he was appointed associate director of the Salt Lake Institute of Religion, which he discharged faithfully until 1975.

He was the author of many studies and articles on the Doctrine & Covenants, the Pearl of Great Price, and Protestant missionary activity, as well as a Priesthood manual on the Apostasy and Restoration. At the time of his death, he was preparing a history of Mormonism during the Nauvoo Period. He worked as a research historian for Nauvoo Restoration, Inc. from 1964-1975, and at some point served as president of both the Salt Lake Historical Society and the Mormon History Association. In 1976, he received the David O. McKay Humanities Award. He served on the high council of the Emigration and East Millcreek Stakes, as well as patriarch of the Salt Lake Canyon Rim Stake. It was while in this capacity that he died in a Salt Lake City hospital on September 20, 1978 at the age of 75.