After graduating from the Faculty of Law at Charles University in 1915, he worked in the civil service in various positions.

From 28 September 1941 to 19 January 1945 he was prime minister, replacing Alois Eliáš, who had supported the underground resistance to the Nazis and was executed.

The most infamous member of his government was Emanuel Moravec, a symbol of Czech collaboration with the Nazis.

Wolf Gruner wrote that Krejčí "enthusiastically paid homage to Nazi rule.

"[1]: 106 His son, Jaroslav Krejčí (1916–2014), was a Czech lawyer, sociologist, and professor at Lancaster University in the United Kingdom.