Pedro Sánchez sworn in as Spain's Prime Minister after ousting Mariano Rajoy

Sánchez, who leads the Spanish Socialist Workers' Party (PSOE), took the oath of office before King Felipe VI at the Zarzuela Palace near Madrid. He chose not to swear on a bible.

The 46-year-old politician faces significant challenges as he assumes office. Spain was riven last year by the Catalan independence crisis, which remains unresolved, and many Spaniards continue to feel the effects of the global economic crisis.

Sánchez -- a pro-European economics professor who was a keen basketball player in his youth -- previously said that he would call for snap elections should he become Prime Minister.

Posting Friday on Twitter, Sánchez promised a fresh start for the country. "Spain starts a new page. A period to recover the dignity of its institutions. From responsibility, dialogue and consensus, it is time to work for equality, to build a country that does not leave anyone behind," he said.

Rajoy, of the Popular Party, on Friday became the first leader in Spain's modern democracy to lose a vote of no confidence in Parliament.

His fate was sealed on Thursday after the Socialists secured support for the no-confidence motion from a number of smaller parties in Parliament, including the Basque Nationalist Party.

The confidence motion was filed by Sánchez after a court convicted Rajoy's former aides of running slush funds to help finance Popular Party election campaigns. The court also questioned the credibility of Rajoy's testimony during the proceedings.

It was the first time in Spain that a party had been convicted and fined on corruption-related charges.