Vajna was a confidant of Prime Minister Ferenc Szálasi, the Hungarian fascist party leader and founder of the extreme right "Party of National Will", which later became the Arrow Cross Party. Vajna was elected Member of Parliament from the regional list of Veszprém County during the 1939 parliamentary election. After the German occupation of Hungary in March 1944, he maintained a good relationship between the Hungarian authorities and the arriving Gestapo and Schutzstaffel officials. He helped to overcoming the resistance fighters and prevent sabotage activities. Following the Arrow Cross Party's coup, Vajna took office as Interior Minister in October 1944 and served until March 1945.