William Cairnes was an Irish politician and merchant.

He was the second son of John Cairnes

John Cairnes (politician)

John Cairnes was an Irish politician.He was the son of Thomas Cairnes and his wife Jane Scott, daughter of John Scott. In 1639, Cairnes was elected as Member of Parliament for Augher, representing the constituency in the Irish House of Commons until the following year.He married Jane Miller,...

 and his wife Jane Miller, daughter of James Miller. His brothers were Alexander Cairnes

Alexander Cairnes

Sir Alexander Cairnes, 1st Baronet was an Irish politician, banker and baronet.-Background:He was the oldest son of John Cairnes and his wife Jane Miller, daughter of James Miller. His younger brother was William Cairnes...

 and Henry Cairnes

Henry Cairnes

Sir Henry Cairnes, 2nd Baronet was an Irish politician, banker and baronet.He was the third and youngest son of John Cairnes and his wife Jane Miller, daughter of James Miller. In 1733, according to a special remainder he succeeded his oldest brother Alexander as baronet. Another brother was...

. In 1703, Cairnes was elected as Member of Parliament

Member of Parliament

A Member of Parliament is a representative of the voters to a :parliament. In many countries with bicameral parliaments, the term applies specifically to members of the lower house, as upper houses often have a different title, such as senate, and thus also have different titles for its members,...

 for Newtown Limavady

Newtown Limavady (Parliament of Ireland constituency)

Newtown Limavady was a constituency represented in the Irish House of Commons until 1800.-1692–1801:...

 and Belfast

Belfast (Parliament of Ireland constituency)

Belfast was a constituency represented in the Irish House of Commons until 1800.-History:Belfast in County Antrim was enfranchised as a borough constituency in 1613...

, representing the latter constituency in the Irish House of Commons

Irish House of Commons

The Irish House of Commons was the lower house of the Parliament of Ireland, that existed from 1297 until 1800. The upper house was the House of Lords...

 until his death in 1707.

Cairnes died without children and was buried at St Michan's Church in Dublin.