Hartley graduated from Arroyo High School in San Lorenzo, California in 1960. He served a mission for The Church of Jesus Christ of Latter-day Saints (LDS Church) in the Eastern States Mission and the Cumorah Mission from 1962 to 1964.

Hartley received both his bachelor's and master's degrees from Brigham Young University (BYU). He did course work towards a Ph.D. at Washington State University.

Hartley is a member of the LDS Church, for which he has served as a member of a stake high council, a Sunday school teacher and a counselor in an elders quorum presidency. He also served for a time as bishop of the Sandy 37th Ward.

Hartley and his wife, the former Linda Perry, are the parents of six children.

Historical work

During the 1970s Hartley worked at the Church History Department, including time as a director of the James H. Moyle oral history project.

Hartley has served as an associate professor of history at BYU. He was also connected with the Joseph Fielding Smith Institute for Latter-day Saint History. In the past Hartley has also served as director of the Family History and Genealogy Research Center at BYU. Besides having taught courses at both BYU and its Salt Lake Center, Hartley has also taught at the LDS Institute of Religion located adjacent to the University of Utah.

Hartley has been active in the Mormon History Association and served as its president in 2000—2001.

Hartley is currently working on the Joseph Smith Papers Project, and is the editor of the first volume with Grant Underwood and Robert Woodford.

Hartley's book My Best For the Kingdom: John Lowe Butler, Mormon Frontiersman won an award from the Association for Mormon Letters in 1994. Hartley's Anson Bowen Call: Bishop of Colonia Dublan which he coauthored with Lorna Call Alder and H. Lane Johnson won the 2008 Mormon History Award for best international Mormon history.