A member of the People's Party (PP), Pérez became a member of the Assembly of Madrid after the May 2003 regional election, in the brief 6th term of the regional legislature, popularly named after the "Tamayazo" scandal. He renovated his seat at the October 2003, 2007, 2011 and 2015 elections. Pérez soon won the confidence of Esperanza Aguirre, becoming a close confidant and collaborator of the then president of the regional government and chairwoman of the regional branch of the PP, the People's Party of the Community of Madrid. He served as spokesperson of the PP parliamentary group in the legislature between 2008 and 2011.