From 1905 to 1907, he served as Assistant United States Attorney for the western district of Missouri, when he resigned to become assistant attorney, United States circuit court at St. Louis.

He resigned this office in 1911 to become special assistant to the Attorney General of the United States, which office he resigned in 1912 to resume the practice of law in St. Louis, Missouri.

He did make one more run for Congress in the 1934 elections; however, he was unsuccessful.

Starting in 1926, he again resumed the practice of law in St. Louis, Missouri, and Washington, D.C. Newton served as general counsel of the Mississippi Valley Association from 1928 to 1943.

He died in Washington, D.C., on September 17, 1945, and was interred in Valhalla Mausoleum, St. Louis, Missouri.