In the election that followed McGuinness's resignation, O'Neill was returned to the Assembly, topping the poll in Mid Ulster and with a 20.6% share of first-preference votes. In March 2017, she called for a referendum on the reunification of Ireland "as soon as possible" in response to the United Kingdom's decision to leave the European Union. O'Neill led the Sinn Féin side in the inter-party negotiations that followed the election, aiming to restore a power-sharing coalition in Northern Ireland, but said at the end of March that the talks had failed, and Sinn Féin would not nominate her for the position of deputy First Minister.