[1] Martínez-Almeida affiliated to the People's Party (PP) when he was 20 years old,[2] and he earned a Licentiate degree in law at the ICADE (Comillas Pontifical University) in 1998.

He left the regional government in 2013 in order to become a member of the General Secretariat and Council of state-owned enterprise SEPIDES (currently SEPI) as Secretary of the Law Division.

In 2017, as Aguirre resigned from her last offices following the detention of her political "dauphin" Ignacio González, Martínez-Almeida replaced her as Spokesperson of the PP's Municipal Group in the City Council.

Martínez-Almeida lost the council election against Manuela Carmena, Más Madrid, but due to a coalition agreement among PP Popular Party, C's Citizens and Vox, he was invested as Mayor on 15 June 2019, during the opening session of the new municipal corporation.

[9] During the campaign, the PP pledged to get rid of the star measure of the previous municipal administration: the low emission zone Madrid Central.

[23] In April 2022, it came to light that his government was involved in a scandal for awarding several contracts to companies managed by aristocrat Luis Medina Abascal, son of Nati Abascal and the Duke of Feria; and his partner, Alberto Javier Luceño Cerón, two businessmen who mediated in the purchase of sanitary material with the Madrid City Council in March 2020, during the worst moment of the COVID-19 pandemic in Spain and a few days after the state of alarm was declared,[24] with whom them both took millionaire commissions for various contracts, being investigated by the Anti-Corruption Prosecutor's Office.