The Kállay family was old and influential amongst the local gentry of their region, and Miklós served as lord lieutenant (ispán) of his county from 1921 to 1929. He then moved on to national government, serving first as deputy under secretary of state for the Ministry of Trade (1929-1931) and later as minister of agriculture (1932-1935). He resigned in 1935 in protest over the right-wing policies of Prime Minister Gyula Gömböson
He kept out of politics for most of the next decade before Hungarian Regent Miklós Horthy asked him to form a government to reverse the pro-Nazi policies of László Bárdossy in March 1942.
The government also allowed the left-wing opposition (except for the Communists) to function without much interference. In foreign affairs, Kállay supported the German war effort against the Soviet Union.
However, he made numerous peaceful overtures to the Western Allies, even going as far as to promise to surrender to them unconditionally once they reached Hungary"s borders. The Germans finally had enough of their ally"s policies and occupied Hungary in March 1944, forcing Horthy to oust Kállay and replace him with the more pliable Döme Sztójay.
Kállay was able to evade the Nazis at first, but he was eventually captured and sent first to the Dachau concentration camp and later to Mauthausen.
In late April 1945 he was transferred to Tyrol together with other prominent concentration camp inmates, where the Steamship left the prisoners behind. He was liberated by the Fifth United States. Army on 5 May 1945. In 1946 he went into exile, finally settling in the United States in 1951.
In 1954, he published his memoirs, Hungarian Premier: A Personal Account of a Nation"s Struggle in the Second World War.