William Stewart, 2nd Viscount Mountjoy, (1675-1728) was an Anglo-Irish peer.

William Stewart was born in 1675 , the son of William Stewart, 1st Viscount Mountjoy. He married Anne Boyle, The daughter of Murrough Boyle, 1st Viscount Blesington

On his death in 1728 his title passed to his son William Stewart, 3rd Viscount Mountjoy, later (1745) William Stewart, 1st Earl of Blessington