In 1909–1912, he was secretary to
Gifford Pinchot, Chief Forester in
Theodore Roosevelt's administration. In 1912–1917, he was Executive Secretary of the
National Conservation Association, appointed by its founder, Pinchot. In 1917–1918, he was Special Assistant to
United States Secretary of the Interior Franklin K. Lane. In 1919–1923, he was Counsel to the National Conservation Association. As part of government efforts to indict big business for the exploitation of the country's natural resources, he was involved in Senate investigations of the Mulhall exposure during Wilson's administration and the
Teapot Dome Scandal of 1921. In 1923–1933, he practiced law in Washington, D.C. In 1925–1929, he was Executive and counsel for the
National Boulder Dam Association. In 1929–1932, he Counsel for the
National Conservation Commission. In 1931–1933, he was Washington, D.C. representative for the
New York Power Authority. In 1933–1938, he was Personal Assistant to
Harold Ickes, Secretary of the Interior, and Assistant to administrator of
Federal Emergency Administration of Public Works. In 1938–1939, Slattery was Under Secretary of the Interior, until his appointment by
Roosevelt on 26 September 1939 to head up the
Rural Electrification Administration (REA). He resigned after a conflict with
Secretary of Agriculture Claude R. Wickard in 1944. The 1944 controversy between the REA and the
Department of Agriculture over the administration of REA led to a Senate investigation. Slattery was involved in the passage of a federal coal and oil leasing measure, federal water power legislation, Alaska coal and home rule acts, and rural electrification legislation. In 1940–1942, he was also Consultant to the power subcommittee of the advisory commission of the Council of National Defense. In 1944, Slattery received
LL.D. from the
University of South Carolina. Slattery was a member of the National Power Policy Committee, the Energy Resources and Land Committees of the
National Resources Planning Board, the Interbureau Coordinating Committee, the Federal States Relations Committee, the
Society of American Foresters, the
National Press Club, the
Missouri Athletic Club, and
Delta Theta Phi fraternity. ==Personal life==