Leonen (born December 29, 1962) is an Associate Justice of the Supreme Court of the Philippines.
He is the second youngest to hold the said position since Manuel V.
Moran in 1938.
Prior to his stint in the country's highest court, he had served as chief peace negotiator of the Republic of the Philippines in the talks with the Moro Islamic Liberation Front.
Leonen was dean of the University of the Philippines College of Law at Diliman from 2008 to 2011.
He is well known in the fields of environmental activism and community organizing.