 He was an attorney with the Law Department of the Title Guarantee and Trust Company in New York City, New York from 1905 to 1913.He was an Assistant United States Attorney for the Southern District of New York from 1913 to 1918.Knox was nominated by President Woodrow Wilson on March 29, 1918, to a seat on the United States District Court for the Southern District of New York vacated by Judge Martin Thomas Manton.