"You will hear the government speak with a sovereign voice. You will see a sovereign foreign policy. You will see professional work," he said during a swearing-in ceremony.
The politician accused the previous government of ignoring many problems and promised that his government would act constructively.
Slovak President Zuzana Caputova swore the veteran politician in for a fourth stint as prime minister and appointed a three-party coalition government on Wednesday.
Fico’s center-left Smer party won the parliamentary election in September on a pledge to end military support for Ukraine.