A member of a noble Protestant family, Horthy entered the Austro-Hungarian naval academy at Fiume (now Rijeka, Croatia) at age 14. Aide-de-camp to the emperor Francis Joseph (1909–14), he distinguished himself as a naval commander in World War I by several times breaking the Allied Adriatic blockade. Promoted to admiral in 1918, he presided over the Austro-Hungarian fleet's transfer to Yugoslavia in October 1918.

The following year, at the request of the counter-revolutionary government at Szeged, Hung., Horthy organized an army to oppose the Communist regime of Béla Kun (Kun, Béla) and led his troops into the capital in November after Kun had fled. The Hungarian Parliament, elected in January 1920, declared for the restoration of the monarchy and elected Horthy regent (March 1). Horthy, however, despite much controversy, thwarted the efforts of King Charles IV to recover his throne.

From 1921 to 1931 Horthy had little to do with public affairs, leaving the conduct of government in the hands of Count István Bethlen. During the troubled 1930s, however, Horthy assumed more and more control, and in 1937 the Parliament voted a considerable extension of his powers. Although he disliked Adolf Hitler, he sympathized with the German dictator's “crusade against Bolshevism,” and initially acquiesced in Hungary's adherence to the German side in World War II. His later efforts to extricate Hungary from the war led to his forced abdication and abduction by the Germans in 1944. He was released by Allied troops in May 1945 and allowed to go to Portugal, where his memoirs, Confidential Papers, were published in 1965.