Montero was chosen by prime minister Pedro Sánchez, following the motion of no confidence that the PSOE presented against the previous government of Mariano Rajoy (PP) and that was approved by the Congress of Deputies on 1 June 2018, to be Finance Minister in new Spanish cabinet. Felipe VI sanctioned by royal decree of June her appointment as holder of the portfolio of Minister of Treasury of Spain. On 7 June she took office as Minister before the King at Palace of Zarzuela.