Graduate in Journalism (UCM, Sciences Po) and in Philosophy (UNED) and master’s graduate in Contemporary Arab Studies (UAM). As a journalist, she has worked at the EFE new agency (first, in the Justice and Interior section in Madrid, and afterwards as a correspondent in Rabat, Morocco) and is also a regular contributor to various publications and media, such as La Marea, La Madeja, Atlántica XXII, La Tribu and Liberoamérica. She was one of the founders and coordinators of the AISH information portal on Arab life. Her doctoral thesis focuses on decolonisation literature and memory in Morocco.

She was also chief content manager at the Instituto 25M Democracia. Casielles held various posts between 2014 and 2017 in the area of Press and Communication with Podemos, during which she was also a member of the Citizen Council. 

As a poet she has had several volumes of her work published, some of which has been included in anthologies translated into other languages.