[2][3] Under the Westminster system, the vacation of a seat by a sitting MP triggers a by-election to choose their successor, with the election date in this case being set by the Secretary of State for Northern Ireland due to Sinn Féin's policy of abstentionism.

[4] Having delayed the announcement in part to avoid a winter election, McGuinness confirmed he had resigned on 30 December 2012,[5] with the formal process of being appointed Crown Steward and Bailiff of the Manor of Northstead occurring on 2 January 2013,[6] a procedural device that Sinn Féin oppose.

[12] Sinn Féin's Francie Molloy MLA, then deputy speaker of the Northern Ireland Assembly,[13] was selected as the party's candidate.

On behalf of the UK Independence Party, David McNarry MLA also supported the idea of a unionist unity candidate in a press release.

[24] On 14 February, the UUP and DUP constituency associations both agreed to support victims' campaigner and local undertaker[25] Nigel Lutton as a single unionist candidate.

[27] However, two UUP Members of the Northern Ireland Legislative Assembly, former deputy leader John McCallister and Basil McCrea, resigned from the party in protest at the decision and closer co-operation with the DUP.

He previously worked as a personal assistant for DUP MP David Simpson, to whom he is related, and had before that been a member of the Young Unionists, the youth wing of the UUP.

[29] Willie Frazer, a victims' campaigner, independent unionist and spokesman for the then newly constituted protest alliance the Ulster People's Forum, initially announced his intention to stand.

[4][30] Frazer told a 'webchat' for the Belfast Newsletter that the Ulster People's Forum "is not a political party", and that in usual circumstances he would consider voting for the Traditionalist Unionist Voice.

[31] At the end of January 2013, Frazer then said he would consider not standing in favour of Jamie Bryson, a leading figure in the Belfast City Hall flag protests who is the interim chair of the Ulster People's Forum.