He was born in Celle. He saw active service during WW I, he was an officer cadet in 1914, by 1915 he was a lieutenant and decorated before becoming a prisoner of war in Russia in October 1915. He returned to Germany in 1920 a convinced Communist to study law at Jena University, becoming a Doctor of law in 1922. From 1924 he worked as a lawyer in Kassel and also as a city councilor for the Volkisch-Social bloc. He joined the Nazi Party in July 1925.
In 1932 he was elected as a National Socialist delegate to the Prussian Landtag, and the next year to the Reichstag. Also in 1933 he was appointed ministerial secretary at the Prussian Ministry of Justice, becoming under-secretary in June 1933. In June 1934, Freisler was named under-secretary in the new Reich and Prussian Ministry of Justice. From 1939, he was instrumental in the creation of special courts for "courts-martial on the domestic front." He was present at the Wannsee Conference as representative for Franz Schlegelberger, the minister in the Reich Ministry of Justice. As President of the Volksgerichtshof (People's Court) from August 1942 (replacing Otto Thierack), the "Hanging Judge" presided over around 1,200 trials, nearly all ended with the death penalty.
He was killed during an air raid on Berlin.