Labor Senator Katy Gallagher leaving the Senate.

There will be another four citizenship by-elections in South Australia, Western Australia, Queensland and Tasmania in coming months in the wake of the High Court's decision this morning to find ACT Labor Senator Katy Gallagher ineligible to have stood in the 2016 election.

Gallagher had sought to renounce her British citizenship ahead of the 2016 election but the process had not been completed by the time she nominated for the election. She had argued to the High Court that she had taken all reasonable efforts to renounce her citizenship and that the failure of the British Home Office to process her renunciation prior to nomination did not prevent her being from constitutionally eligible even under the High Court's much stricter reading of section 44 of the constitution enunciated last year.