William Pearse (1881 - May 4, 1916) was an Irish nationalist and younger brother of Patrick Pearse. Throughout his life, Willie lived in the shadow of his brother to whom he was devoted. They had a close, almost puerile, relationship. He was trained to take over his father's stonemason business, but gave it up to help Patrick run St. Enda's School which he founded in 1908. Willie was involved in the arts and theater at St. Enda's and aided the overall running of the school.

Willie followed his brother into both the Irish Volunteers and the Irish Republican Brotherhood. He took part in the Easter Rising in 1916, staying by his brother's side at the General Post Office. Following the surrender he was court martialed and sentenced to be shot. It has been said that as he was only a minor player in the struggle it was his surname that condemned him. However, at his court martial Willie rather trumpeted his involvement, exaggerating it even, and perhaps condemned himself.

On May 3 William Pearse was granted permission to visit his brother in Kilmainham Jail, to see him for the final time. However, while Willie was en route, Patrick Pearse was shot. Willie followed his brother the next day.