In May 1850, judge Orville C. Pratt of the Oregon Supreme Court appointed Prichette to serve as defense counsel for the Native Americans charged with the Whitman Massacre at their trial in Oregon City, Oregon after the Cayuse War. Shortly after the trial, Prichette was sworn in as governor. According to the account of U.S. Marshall Joseph Meek, Prichette ordered Meek to free the five convicted natives. But Meek refused, on the grounds that former governor Lane had already signed their death warrants, and he carried out the executions.