Born to a Quaker family near White Haven, Pennsylvania, on May 4, 1872, A. Mitchell Palmer attended a Moravian parochial high school in Bethlehem, Pennsylvania, graduating later from Swarthmore College in 1891. He began working as the official stenographer of the Forty-third Pennsylvania Judicial District in 1892. Palmer studied law while working as a stenographer and was admitted to the Pennsylvania state bar in 1893.

He entered national politics while a member of the Democratic state executive committee, winning a congressional seat from the Twenty-sixth Congressional District in 1908. He was re-elected twice, serving as the House Democratic Caucus chairman during his last term. Palmer ran unsuccessfully for the U.S. Senate in 1914, later declining an appointment as an appellate justice on account of a low salary. President Woodrow Wilson appointed him to the post of Alien Property Custodian on October 22, 1917; in that position, Palmer oversaw and confiscated the property of German-Americans during World War I.When Attorney General Thomas Gregory resigned in March 1919, Wilson sought to appoint someone other than Palmer to the post. Failing in that matter, Wilson tapped Palmer to head the Justice Department; he would remain in that post until the end of the Wilson administration. Palmer initiated a series of raids on "subversive" elements in American society -- many of them Communists and Socialists -- touching off what came to be known as the "Red Scare." Following his time in government, Palmer returned to his law practice, dying on May 11, 1936.