Cowan was raised in Los Angeles. He is legally blind and has had retinitis pigmentosa since birth, and by 2000 he had lost nearly all vision. Halfway through his undergraduate and graduate degrees, Cowan served a mission for the LDS Church in the Spanish-American mission, among the Mexican immigrants in Texas and New Mexico from 1953 to 1956. On his mission he met Dawn Houghton, and they later married and had six children.
Beginning in 1961 Cowan was a professor of Church History and Doctrine at BYU. Cowan received BYU's professor of the year award in 1965. He has taught at the BYU Jerusalem Center and in the spring of 2007 was a visiting professor at BYU-Hawaii. He retired from BYU in 2015.
Church positions
Among other positions in the Church Cowan has served as a stake patriarch.
Writings
Cowan helped write the LDS Church's Sunday School manual from 1978–80, on the Doctrine and Covenants and LDS history. In 1972 the LDS Church planned a new sixteen-volume sesquicentennial history to be published in 1980, and Cowan was commissioned to write about the 20th century. These contracts were all canceled in 1981 but Cowan still completed and published his volume, as The Church in the Twentieth Century in 1985. From 1981-1993 Cowan served as the chair of the committee in charge of preparing gospel doctrine lessons for the LDS Church. Among his books are Temples to Dot the Earth, California Saints, A 150-year Legacy in the Golden State; The Church in the Twentieth Century ; The Latter-day Saint Century which covered about the same topic but was written 15 years later. He also co-wrote a book about the international church with Donald Q. Cannon. Cowan, along with Cannon and Arnold K. Garr was one of the editors of the Encyclopedia of Latter-day Saint History. He wrote the article on the history of the Church from 1945 until 1990 for the Encyclopedia of Mormonism. He also wrote the articles for History of Temples, Missionary Training Centers, Branch, and Branch President. He was a co-editor with John P. Livingstone and Craigh J. Ostler of The Mormons: An Illustrated History of the Church of Jesus Christ of Latter-day Saints published in 2013. In 2015 BYU's religious studies center published his Provo's Two Temples book.