Krejčí was born on 27 June 1892 in Křemenec, Moravia, Austria-Hungary. After graduating from the Faculty of Law at Charles University in 1915, he worked in the civil service in various positions. During the 1930s, he also lectured on constitutional law at Masaryk University (from 1938 as a professor).
^Gruner, Wolf (2015). "Protectorate of Bohemia and Moravia". In Gruner, Wolf; Osterloh, Jörg (eds.). The Greater German Reich and the Jews: Nazi Persecution Policies in the Annexed Territories 1935-1945. War and Genocide. Translated by Heise, Bernard. Berghahn Books. pp. 99–135. ISBN978-1-78238-444-1.