Spell in politics
Cantó joined Ciudadanos in 2006 and ran as a candidate for the local list Vecinos por Torrelodones in the 2007 municipal elections. He later joined Union Progress and Democracy (UPyD) in 2008.
In 2011, Cantó was selected to head the UPyD list in Valencia Province for the 2011 general election, where he gained a seat. In 2014, he was selected as UPyD candidate for President of the Valencian Government in the 2015 regional elections. He resigned his seat in Congress in April 2015 and announced that he would also not be standing for president in the Valencian regional elections. In his resignation announcement he stated that he would consider whether to remain in UPyD after the party's congress in June 2015.
Cantó had been one of the UPyD figures most critical of the leadership of Rosa Díez. Following poor local and regional election results, Díez resigned and Cantó supported Irene Lozano in the subsequent leadership election on 12 July 2015, in which Lozano lost to Andrés Herzog. 4 days later, Cantó announced that he would sit as an independent and would seek the number two position on the Citizens' list for the 2015 Spanish general election. He was chosen as the second candidate and was elected to Congress in the 2015 election.
He ran as Cs' candidate for the 2019 Valencian regional election, and was elected to the Corts Valencianes, becoming the leader of his parliamentary group and one of the most conspicuous legislators. Some of his speeches went viral. He hired a cyberactivist and adherent of the so-called alt-right as aid, who helped him to nurture further popularity. Following an ephemeral rapprochement with the Valencian government majority during the early stages of the COVID-19 pandemic, Cantó returned to an all-out style of opposition, going further than Vox and the PP in some stances.
Following the announcement of the motion of no confidence in the PP regional government in Murcia in March 2021 (and ensuing crisis in Cs as party regional legislators who had initially backed the motion crossed the floor within hours to accept government posts offered by the PP), PP's Secretary General Teodoro García Egea contacted Cantó. Cs' leader Inés Arrimadas proposed including Cantó in the executive board of Cs, yet Cantó announced he was leaving the party and his seat on 15 March 2021.
9 days later, on 24 March 2021, PP announced Cantó would be on their list for the 2021 Madrilenian regional election. However, Cantó was registered in the Valencian Community (so he could run as a candidate in the Valencian regional election) and the electoral body is set by the national electoral law (LOREG) at two months before elections are called, so doubts were cast about Cantó's passive suffrage availability, as it requires active suffrage. He claimed he had registered in the Madrid region "some days ago". In April 2021, the Administrative Court number 5 of Madrid resolved that Cantó, along with fellow intended candidate Agustín Conde, was "ineligible" for the PP list due to not having registered in the Madrid region in due time and form.
In 2021, Cantó joined the Madrid-based ISSEP, a far-right educational centre founded in Spain by Marion Maréchal, to lecture on speaking skills.
