Willie started playing the whistle at age 5, and later took up the flute. He first saw a set of pipes in 1936 when he saw Johnny Doran playing locally. He obtained his first set of pipes two years later. His influences included Leo Rowsome, Séamus Ennis, John Potts, and Andy Conroy. Clancy won the Oireachtas competition in 1947. Unable to earn a living from music he emigrated to London where he worked as a carpenter.
Returning to Milltown Malbay in 1957 he recorded some influential 78 rpm recordings for the Gael Linn label - among them the classic reel selection "The Old Bush/The Ravelled Hank of Yarn." The next decades he stayed in Milltown Malbay.
Clancy married Dóirín Healy in 1962. The Willie Clancy Summer School was established in his honour in 1973, by Clancy's friends Junior Crehan, Martin Talty, Sean Reid, Paddy Malone, Paddy Mc Mahon, Frankie McMahon, Jimmy Ward, JC Talty, Harry Hughes, Michael O Friel Séamus Mac Mathúna and Muiris Ó Rócháin. He was also the subject of a major television documentary "Cérbh É? Willie Clancy" on TG4, first broadcast in November 2009. In this programme, one of a series in which major figures in contemporary traditional music, profile and pay homage to a master of their craft from a bygone age, Peter Browne traced the life and legacy of Clancy.