William Stewart Collis (27 September 1860 — 2 January 1947) was an Irish international rugby union player.
A Dublin solicitor, Collis played rugby during his youth and received an Ireland cap in 1884, playing as a forward against Wales at Cardiff. He was the head of Collis & Ward Solicitors.
Collis's son Robert was also an Ireland rugby international. Robert's twin brother was the writer John Stewart Collis and another son, Maurice Collis, was a colonial administrator in Burma.