The 1986 by-election in Newry and Armagh was caused by the resignation of incumbent Member of Parliament Jim Nicholson.
Nicholson, along with all sitting Unionist MPs, resigned their Westminster seats in December 1985, to highlight their opposition to the Anglo-Irish Agreement and to use the resultant by-elections to campaign on the issue.
The poll was held on January 23, 1986, however Nicholson was not re-elected, losing his seat to the nationalist SDLP candidate Seamus Mallon. Nicholson also failed to recapture the seat at the following general election.
| Newry and Armagh by-election, 1986 | |||||
|---|---|---|---|---|---|
| Party | Candidate | Votes | % | ±% | |
| SDLP | Seamus Mallon | 22,694 | |||
| Ulster Unionist | Jim Nicholson | 20,111 | |||
| Sinn Féin | Jim McAllister | 6,609 | |||
| Workers' Party | Patrick McCusker | 515 | |||
| Majority | 2,583 | ||||
| SDLP gain from Ulster Unionist | Swing | ||||
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