John Gordon Swift MacNeill (11 March 1849 – 24 August 1926) was an Irish Protestant Nationalist politician and MP, in the House of Commons of the United Kingdom of Great Britain and Ireland for South Donegal from 1887 until 1918, Professor of Constitutional and Criminal Law at the King's Inns, Dublin, 1882–88, and Professor of the Law of Public and Private Wrongs at the National University of Ireland from 1909.

At the subsequent four general elections he was returned unopposed, but in 1918 he was deselected as Irish Party candidate in favour of John T. Donovan, who in turn lost the seat to Sinn Féin.

In parallel with his pursuit of Home Rule for Ireland, many of his efforts were devoted to improving the governance of the United Kingdom.

In 1890 he took an unpopular stance in opposing the cession to Germany of Heligoland, which became an important German naval base in the First World War.

The Times commented 'his learning was allied to a disposition of quite an explosive kind, which, when he was on his feet, made him shout and gesticulate and twist about into many odd shapes and forms'.

They do however contain an important account of MacNeill's discussions with Cecil Rhodes in 1887–88 which led to the latter's donation of £10,000 to the Irish Party and to the election of James Rochfort Maguire to Parliament.