Horton, 47, will serve out the rest of Trout's term, which ends in January 2009.
Horton has served in the 4th Judicial District since 1996, and was previously an Ada County magistrate, a deputy state attorney general and a deputy Ada County prosecutor. He also served as legislative council for the Idaho Prosecuting Attorneys Association.
A Nampa native, Horton has a bachelor's degree from the University of Washington, and earned his law degree at the University of Idaho.
With the appointment, he will earn $114,900.
This is the second Supreme Court appointment Gov. Otter has made this year, earlier selecting Warren Jones to fill the position left by Justice Gerald Schroeder.
While Horton's appointment fills out the court roster, it also means there are no longer any women serving on the court.