In December 2016, Cosidó returned to the Senate, as he was designated Senator by the Cortes of Castile and León, with the sole support in the regional parliament from the PP's parliamentary group. After the ascension of Pablo Casado to the presidency of the People's Party (now in the opposition after the successful vote of no confidence in Mariano Rajoy) in the summer of 2018, the new PP leader appointed Cosidó as Spokesperson of the PP parliamentary group in the Spanish Upper house, where the party enjoyed an absolute majority of senators.