 A Republican, Parker was appointed to serve on the Territorial Supreme Court on January 10, 1898 by President William McKinley, on the recommendation of territorial governor Miguel Antonio Otero.He was reappointed to the Territorial Supreme Court by President Theodore Roosevelt in 1901 and 1905, and by William Howard Taft in 1909.While serving as a territorial district court judge, he presided over two trials that received national publicity.