Justice Oswald Leslie De Kretser III was a Ceylonese (Sri Lankan) judge. He was a judge of the Supreme Court of Ceylon. Born to Oswald Leslie De Kretser II a Puisne Justice of the Supreme Court of Ceylon, he was educated at the Royal College, Colombo. There he won the Governors Prize for Latin Prose, Director's Prize for Classics, the Harward Prize for Ancient History and Cecil Perera Prize for History. Entering the University College, Colombo in 1928, he gained a BA from the University of London and became a proctor in 1937.