Northern Ireland is divided into 18 parliamentary constituencies: 4 borough constituencies in Belfast and 14 county constituencies elsewhere. Section 33 of the Northern Ireland Act 1998 provides that the constituencies for the Northern Ireland Assembly are the same as the constituencies that are used for the United Kingdom Parliament.^[1] Parliamentary constituencies are not used for local government, which is instead carried out by 11 district councils; these often have different boundaries.

Constituencies

Each constituency returns one Member of Parliament (MP) to the House of Commons at Westminster and five Members of the Legislative Assembly (MLAs) to the devolved Northern Ireland Assembly at Stormont. Six MLAs were returned per constituency until the Assembly Members (Reduction of Numbers) Act (Northern Ireland) 2016 reduced the number to five, effective from the 2017 Assembly election.^[2]

2019 general election

  Democratic Unionist   Sinn Féin   Social Democratic and Labour   Ulster Unionist   Alliance Party

Name[nb 1]	Electorate[3]	Majority[nb 2]	Member of Parliament		Unionist %	Nationalist %	Other %	Map
Belfast East BC	66,245	1,819		Gavin Robinson	55.1	0.0	44.9
Belfast North BC	72,225	1,943		John Finucane	43.1	47.1	9.8
Belfast South BC	69,984	15,401		Claire Hanna	27.2	58.4	14.3
Belfast West BC	65,644	14,672		Paul Maskey	13.5	65.7	20.9
East Antrim CC	64,830	6,706		Sammy Wilson	62.8	8.1	29.1
East Londonderry CC	69,246	9,607		Gregory Campbell	49.3	35.7	15.1
Fermanagh & South Tyrone CC	72,848	57		Michelle Gildernew	43.2	50.1	6.3
Foyle CC	74,346	17,110		Colum Eastwood	12.4	82.0	5.5
Lagan Valley CC	75,735	6,499		Jeffrey Donaldson	64.9	6.3	28.8
Mid Ulster CC	70,449	9,537		Francie Molloy	30.4	60.2	9.4
Newry & Armagh CC	81,226	9,287		Mickey Brady	30.0	61.8	8.3
North Antrim CC	77,134	12,721		Ian Paisley, Jr.	65.9	19.5	14.7
North Down CC	67,099	2,968		Stephen Farry	45.2	0.0	54.8
South Antrim CC	71,711	2,689		Paul Girvan	64.3	16.7	19.1
South Down CC	79,175	1,620		Chris Hazzard	21.9	64.1	13.9
Strangford CC	66,928	7,071		Jim Shannon	62.6	6.8	30.5
Upper Bann CC	82,887	8,210		Carla Lockhart	53.4	33.8	12.9
West Tyrone CC	66,259	7,478		Órfhlaith Begley	28.7	60.4	11.0

Data from the BBC Election Website. For full official results see the Electoral Office of Northern Ireland.

Historical representation by party

Where a cell is marked → (with a different colour of frame to the preceding cell) it indicates that the previous MP continued to sit under a new party affiliation. Changes are dated in the header row: either a general election (four-figure year, bold, link) or by-election or change in affiliation (two-figure year, italic, link or details appear on hover).

1801 to 1832 (22 MPs)

Antrim

  Tory   Whig

Londonderry

  Tory   Whig

* Sir George Hill, 2nd Baronet, was elected to sit as MP for both Coleraine and Londonderry City in the 1806 general election and chose to continue to sit for Londonderry City, hence the 1807 by-election, in which Walter Jones was restored to his seat.

Tyrone

  Tory   Whig   Independent

* At both the 1802 and 1806 elections, George Knox was returned for both Dungannon and Dublin University and chose to sit for the university seat.

Armagh

  Tory   Whig

* Charles Brownlow was initially elected as a Tory but at some point changed his affiliation to sit with the Whigs.

Down

  Tory   Whig

* The Parliaments of England by Henry Stooks Smith suggests that after the 1806 election there was a petition, which led to Edward Southwell Ruthven (Whig) being unseated and John Wilson Croker (Tory) being declared duly elected. Parliamentary Election Results in Ireland, 1801–1922, edited by BM Walker, does not make any reference to such a petition.

Fermanagh

  Tory

1832 to 1885 (29 MPs)

Antrim

  Conservative   Whig   Peelite   Liberal

Londonderry

  Conservative   Whig   Liberal

*unseated on petition

Tyrone

  Conservative   Peelite   Liberal

Armagh

  Conservative   Whig   Peelite   Liberal

Down

  Conservative   Whig   Peelite   Liberal

Fermanagh

  Conservative

1885 to 1918 (25 MPs)

Antrim

   Conservative Party    Irish Unionist then Ulster Unionist    Russellite Unionist    Independent Unionist

Armagh

   Conservative Party    Irish Unionist then Ulster Unionist    Irish Parliamentary Party (1885-90, 1900-22) / Irish National League (1890-1900)    Irish National Federation    Healyite Nationalist    Nationalist Party

Belfast

   Conservative Party    Irish Unionist then Ulster Unionist    Independent Unionist    Liberal Unionist    Irish Parliamentary Party (1885-90, 1900-22) / Irish National League (1890-1900)    Irish National Federation    Nationalist Party    Labour Unionist

Down

   Conservative Party    Irish Unionist then Ulster Unionist    Russellite Unionist    Irish Parliamentary Party (1885-90, 1900-22) / Irish National League (1890-1900)    Irish National Federation    Nationalist Party

Fermanagh

   Irish Unionist then Ulster Unionist    Russellite Unionist    Irish Parliamentary Party (1885-90, 1900-22) / Irish National League (1890-1900)    Irish National Federation

Londonderry

   Conservative Party    Irish Unionist then Ulster Unionist    Liberal Unionist    Liberal Party    Irish Parliamentary Party (1885-90, 1900-22) / Irish National League (1890-1900)    Irish National Federation

Tyrone

   Conservative Party    Irish Unionist then Ulster Unionist    Russellite Unionist    Liberal Unionist    Liberal Party    Irish Parliamentary Party (1885-90, 1900-22) / Irish National League (1890-1900)    Irish National Federation    Nationalist Party

1918 to 1922 (30 MPs)

   Irish Unionist then Ulster Unionist    Independent Unionist    Labour Unionist    Sinn Féin

1922 to 1950 (13 MPs)

  Ulster Unionist   Ulster Progressive Unionist   Independent Unionist   New Party   Northern Ireland Labour   Independent Labour   Federation of Labour   Irish Labour   Nationalist Party

1950 to 1983 (12 MPs)

Periodic boundary reviews commenced in 1947.^[4][5] The elections at which these were implemented are tagged with diamond suit characters, ♦.

The 1st Periodic Review boundary map can be viewed on the ARK elections website. Changes in the 2nd review were relatively minor.^[6]

Notes:

1. The constituency was won by Philip Clarke of Sinn Féin, but he was unseated on petition on the basis that his criminal conviction (for Irish Republican Army activity) made him ineligible. Instead, the seat was awarded to the Ulster Unionist Party (UUP) candidate.
2. The seat was originally won by Tom Mitchell of Sinn Féin, but Mitchell was subsequently unseated upon petition, on the grounds that his terrorist convictions made him ineligible to sit in Parliament. The seat was awarded to Charles Beattie of the UUP. However, Beattie in turn was also found ineligible to sit due to holding an office of profit under the crown, triggering a further by-election.
3. Original winner of the 1950 election in that seat, James Godfrey MacManaway (UUP), disqualified due to being a clergyman. Teevan won the subsequent by-election

1983 to present (17, then 18 MPs)

3rd and 4th Review boundary maps can be viewed on the ARK elections website: 1983, 1997.

  Democratic Unionist   Sinn Féin   Social Democratic and Labour   Ulster Unionist   Alliance Party   Independent   Ulster Popular Unionist   UK Unionist Party

¹Paisley Jr was suspended from the DUP between July and November 2018.

Seats by political alignment (1983–present)

Proposed boundary changes

The Boundary Commission for Northern Ireland submitted their final proposals in respect of the Sixth Periodic Review of Westminster Constituencies (the 2018 review) in September 2018. Although the proposals were immediately laid before Parliament they were not brought forward by the Government for approval. Accordingly, they did not come into effect for the 2019 election which took place on 12 December 2019, and which was contested using the constituency boundaries in place since 2010.

Under the terms of the Parliamentary Voting System and Constituencies Act 2011, the Sixth Review was based on reducing the total number of MPs from 650 to 600 and a strict electoral parity requirement that the electorate of all constituencies should be within a range of 5% either side of the electoral quota.

On 24 March 2020, the Minister of State for the Cabinet Office, Chloe Smith, issued a written statement to Parliament setting out the Government's thinking with regard to parliamentary boundaries. Subsequently, the Parliamentary Constituencies Act 2020 was passed into law on 14 December 2020. This formally removed the duty to implement the 2018 review and set out the framework for future boundary reviews. The Act provided that the number of constituencies should remain at the current level of 650, rather than being reduced to 600, while retaining the requirement that the electorate should be no more than +/- 5% from the electoral quota.

The Act specified that the next review should be completed no later than 1 July 2023 and the Boundary Commission formally launched the 2023 Review on 5 January 2021. The Commission calculated that the number of seats to be allocated to Northern Ireland will be unchanged, at 18.

See 2023 Periodic Review of Westminster constituencies for further details.