Joel Horton was born in Nampa, Idaho in 1959. He graduated from Borah High School in Boise before attending the University of Washington. He received a B.A. in Political Science in 1982 and his J.D. from the University of Idaho College of Law in 1985.
Justice Horton practiced law in Lewiston for one year before marrying future Ada County Magistrate Carolyn Minder and moving to Twin Falls. He was a deputy prosecuting attorney in Twin Falls from 1986 - 1988. He worked as a criminal deputy with the Ada County Prosecutor for three years before becoming a Deputy Attorney General in 1991. He returned to the Ada County Prosecutors Office in 1992, serving as a deputy criminal prosecutor until 1994.
In 1994, Justice Horton was appointed Ada County magistrate, serving as a family law judge until his appointment to the district court in 1996 by Governor Phil Batt. He served as a district judge until his appointment to the Idaho Supreme Court. In September of 2007, Governor C. L. "Butch" Otter appointed Justice Horton to succeed Justice Linda Copple Trout.