Judge Gratton was born and raised in Emmett, Idaho. He attended Boise State University, graduating in 1982 with a B.A. in Political Science. Judge Gratton received a Juris Doctor from the University of Idaho College of Law in 1985.
He served as an intern law clerk for Ninth Circuit Judge J. Blaine Anderson in 1984 and as a law clerk to United States District Court Judge Harold L. Ryan from 1985 to 1987. Judge Gratton joined the law firm of Evans Keane LLP in 1987, becoming a partner in 1993, until his appointment to the Idaho Court of Appeals in 2009, by Governor C.L. "Butch" Otter.
Judge Gratton and his wife, Robin, have three children, John (deceased), Kevin and Breanne.