Tentatively intended to run 62nd in the PP list for the 2015 Madrilenian regional election, his position was ultimately upgraded to the 51st place of the list, at the expense of Tomás Serrano. He was not elected either. 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. He left his seat in the regional legislature in 23 November 2016, following his appointment as Director-General of Environment of the regional government. 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.