During both World Wars I and II, Walter was in the air service of the United States Navy.

[1] Walter is best known for the McCarran-Walter Act, passed over President Truman's veto in 1952, which, while it opened naturalization to Asian immigrants for the first time, continued the immigration quota system based on national origin introduced in 1924, and allowed the U.S. government to deport and/or bar from re-entry those identified as subversives, particularly members and former members of the Communist Party.

In 1944, he presented President Roosevelt with a letter opener made of an arm bone of a fallen Japanese soldier.

Walter also served as a director of the Pioneer Fund, a foundation best known for its advocacy of IQ variation among races.

Walter appeared in a central role in the 1960s-era U.S. government anti-Communist propaganda film Operation Abolition.