Historically a unionist area, North Down is currently represented by Alex Easton 1885–1918: The baronies of Castlereagh Lower, Lower Ards, and Upper Ards, that part of the barony of Castlereagh Upper in the parishes of Comber and Knockbreda, and that part of the parliamentary borough of Belfast lying in County Down.

In January 1980, the Boundary Commission's original proposals suggested significantly reducing the size of the constituency and renaming it 'Loughside' on the grounds that this would avoid confusion in the event of borough council elections being held on the same day.

As a result, in 1983 the seat was radically cut down as part of an expansion of Northern Ireland's constituencies from 12 to 17, although the name remained unaltered.

In boundary changes proposed by a review in 1995, the seat exchanged territory with Strangford, losing the Dundonald area from Castlereagh and gaining a part of Ards.

Sinn Féin contested the general election of 1918 on the platform that instead of taking up any seats they won in the Imperial Parliament, they would establish a revolutionary assembly in Dublin.

These shares of the popular votes are the highest ever achieved in a United Kingdom general election (post 1832 Reform).

Traditionally levels of turnout in elections are very low by Northern Ireland standards, possibly because the lack of a serious threat of a nationalist victory removes the impetus to vote common among unionists elsewhere in the province.

In 1977 he left the Ulster Unionists in protest over their increasing support for Enoch Powell's proposed policy of integration for Northern Ireland, rather than the restoration of devolved government.

Standing as an independent Unionist, Kilfedder successfully defended his seat against a UUP challenge in the 1979 general election.

As part of his platform for integration, McCartney had called for the major UK parties to organise and stand in the province and his result gave impetus to this campaign.

They stood candidates in several Northern Ireland constituencies in the 1992 general election, but their strongest prospect was expected to be North Down.

The local Assembly member Peter Weir was selected, but his opposition to the Good Friday Agreement and David Trimble's leadership became very prominent and a running source of embarrassment to the party.

In the 2003 Assembly election Weir successfully defended his seat for the DUP, who also gained another MLA from the Northern Ireland Women's Coalition.

In a strong contest, Hermon retained the seat, becoming at that time the only Ulster Unionist MP, though she later left that party.

In the 2024 United Kingdom general election in Northern Ireland, former MLA for North Down (Assembly constituency) Alex Easton succeeded in capturing the seat from Stephen Farry, defeating him in a landslide, with the backing from the DUP and Traditional Unionist Voice, running as an Independent Unionist.

Sylvia Hermon resigned the UUP whip in 2010, in protest against that party's electoral pact with the NI Conservatives to form UCU-NF.

In 1980 Kilfedder formed the small Ulster Popular Unionist Party and contested all subsequent elections under this label.