William Sears (died 23 March 1929) was an Irish Sinn Féin and later Cumann na nGaedhael politician.
He was elected as a Sinn Féin MP for the Mayo South constituency at the 1918 general election. In January 1919, Sinn Féin MPs refused to recognise the Parliament of the United Kingdom and instead assembled at the Mansion House in Dublin as a revolutionary parliament called Dáil Éireann, though Sears did not attend as he was in prison. He was elected unopposed as a Sinn Féin Teachta Dála (TD) for the Mayo South–Roscommon South constituency at the 1921 elections.
He supported the Anglo-Irish Treaty and voted for it. He was re-elected unopposed for the same constituency at the 1922 general election, this time as a pro-Treaty Sinn Féin TD. He was elected as a Cumann na nGaedhael TD for Mayo South constituency at the 1923 general election. He lost his seat at the June 1927 general election but was elected to the Seanad in 1928.