The North Roscommon by-election of 1917 was held on 3 February 1917. The by-election was held due to the death of the incumbent Irish Parliamentary MP, James Joseph O'Kelly. It was won by the Sinn Féin candidate Count George Noble Plunkett, the father of Joseph Plunkett who was shot for his role in the Easter Rising.
It was Sinn Féin's first victory for a Parliamentary election and would presage the virtual clean sweep of Southern Irish seats in the 1918 general election in Ireland.
References
North Roscommon by-election, 1917 Wikipedia(Text) CC BY-SA