Catalan authorities announced their new cabinet on Friday, paving the way for Madrid to end direct rule over the region by excluding four nominees under investigation for their role in its independence drive.
"This government is committed to moving to an independent state in the form of republics", said Kim Torr during the oath.
Mr. Torra later called for talks with Spain's new Prime Minister.
It took several tense months after the snap elections for the Catalan nationalists to finally get approval for a new regional government, after several failed attempts when Madrid barred jailed candidates or those in self-imposed exile, such as former regional leader Carles Puigdemont, from office.
Less than two hours after Sanchez had taken his oath to uphold the Spanish Constitution, Catalan chief Quim Torra demanded to meet with Sanchez and speak "government to government" regarding the future of the wealthy yet restive northeastern region.
Puigdemont fled to Belgium in October 2017 to avoid charges after the Catalan parliament declared independence following a referendum deemed illegal by Madrid.
Sanchez himself called Torra "the Spanish Le Pen" in aligning him with the most extreme elements of the European far-right.
He took power after a no-confidence vote in his People's Party predecessor Mariano Rajoy.
A court in northern Germany had allowed Puigdemont, Catalonia's former regional president, to leave jail on bail shortly after he was detained March 25 at Spain's request.
Socialist leader Pedro Sanchez has been sworn in as Spain's prime minister by King Felipe VI. The outgoing Rajoy's reputation was ruined by a corruption case within his Popular Party and aided by Catalonia's push for independence.
Mr Sánchez's centre-Left PSOE won Friday's no-confidence motion with the support of the hard-Left party Podemos, Catalan pro-independence parties and Basque nationalists - generating speculation over what Mr Hernando claimed were "shady backroom deals" that had yet to be revealed.
Theoretically, Sanchez will govern until mid-2020, when the parliamentary election is held.