He was an Assistant United States Attorney for the Eastern District of Louisiana from 1905 to 1908.

He was the United States Attorney for the Eastern District of Louisiana in 1908.

[1] Foster was nominated by President Theodore Roosevelt on January 22, 1909, to a seat on the United States District Court for the Eastern District of Louisiana vacated by Judge Eugene Davis Saunders.

He was confirmed by the United States Senate on February 2, 1909, and received his commission the same day.

[1] Foster was nominated by President Calvin Coolidge on January 3, 1925, to a seat on the United States Court of Appeals for the Fifth Circuit vacated by Judge Alexander Campbell King.