Pratt was born in Monterrey, Mexico to Mormon parents. His family later moved to Colonia Dublán. In 1947, the family moved to Lehi, Arizona. From 1961 to 1963 Pratt served as a LDS Church missionary in Argentina. He received a bachelor's degree from the University of Arizona and a law degree from Arizona State University.
In 1968, Pratt baptized Karen Ann Yeoman, who he had known for several years. She was a graduate of Arizona State who had taken institute classes there with Rhett James. In 1969, Pratt married Yeoman in the Mesa Arizona Temple. They have eight children.
In 1971 and 1972 Pratt was a law clerk for Judge David Lewis of the United States Court of Appeals for the Tenth Circuit. Pratt worked for the Salt Lake City law form of Kirton and McConkie. In this position, he worked as an attorney for the LDS Church. He was employed as general counsel for the church in the South America North Area of the church at the time of his call as a general authority.
From 1985 to 1988 Pratt served as a Regional Representative of the Twelve in Ecuador. From 1988 to 1991 he served as president of the church's Spain Seville Mission. From 1995 to 1997, Pratt was an area seventy. In 1997, he was called as a member of the church's First Quorum of the Seventy.