He was however appointed as Chief of Staff of Ana Botella in 2010, when she was the Delegate of Environment of the Madrid Municipal Government, entering the politics of the City Council.

Nonetheless, he became member of the city council in the 2011–2015 term, as he replaced on 17 January 2012 the vacant seat left by Pilar Martínez.

[9] A close collaborator of Botella, who had become Mayor in December 2011 (to the point Sanjuabenito was considered "shadow Vice Mayor"),[3] Sanjuanbenito became the Delegate of Environment and Mobility of the municipal government on 10 May 2013, replacing Juan Antonio Gómez-Angulo,[10] as the Constitutional Court had ruled against the designation as members of the government board of individuals not elected to the city council (as it was the case of Gómez-Angulo), declaring the appointments void.

He became a member of the 10th term of the Assembly of Madrid on 9 July 2015, replacing the vacant seat of José Tortosa de la Iglesia.

Following the investiture of Ángel Garrido as president of the Community of Madrid in May 2018, Sanjuanbenito was appointed as Vice-Minister of Humanization of Healthcare Assistance.