Prof Ordejón is Director of the Catalan Institute of Nanoscience and Nanotechnology (ICN2). He earned his degree in Physics (1987) and PhD in Science (1992) at the Universidad Autónoma de Madrid. He worked as a postdoctoral researcher at the University of Illinois at Urbana-Champaign (USA) from 1992 to 1995, and as assistant professor at the Universidad de Oviedo from 1995 to 1999. In 1999 he obtained a research staff position at the Institut de Ciència de Materials de Barcelona (ICMAB-CSIC). In 2007 he moved to CIN2 (now ICN2) as the leader of the Theory and Simulation Group, where he is currently a Distinguished Researcher and Director.

He is known for being one of the main developers of the popular SIESTA software for first-principles calculations. He has published more than 200 scientific articles, which have received over 30,000 citations (h-index of 60). Since 2009 he has served as co-editor of EPL (formerly Euro Physics Letters) and since 2004 as regional editor of physica status solidi. He oversaw the Condensed Matter Physics subject area of the Physics Panel of the Spanish National Evaluation and Foresight Agency (ANEP) from 2003 to 2006, and was the head of the Physics and Engineering Panel of the Access Committee to the Spanish Supercomputing Network from 2005 to 2011. He became a fellow of the American Physical Society in 2005, and in 2017 was elected a member of the Academia Europaea.