Although not from a Roman Catholic Irish background, Parnell is renowned in Irish history for his efforts to bring about a more emancipated country and was the great-grandfather of Charles Stewart Parnell, leader of the Irish Home Rule campaign. Parnell first served in the Parliament of Ireland as one of the members for Bangor, from 1767 to 1768. He later sat for Queen"s County from 1783 until the Union with Great Britain created the United Kingdom of Great Britain and Ireland in 1801.
After the Union, he gained a seat in the Parliament of the United Kingdom for a short time as member for Queen"s County, but died in December of the same year.
From a line of politically astute ancestors who had moved to Ireland in the 17th century, Parnell rose to the highest positions in Irish politics as Commissioner of the Revenue (1780), Chancellor of the Exchequer (1787), and Lord of the Treasury (1793). He died suddenly in London in 1801.
Before this, Parnell was a Commander of Irish Volunteers and had been instrumental in winning the right for Irish Roman Catholics to vote and to be elected to Parliament. However, the latter faltered when the parliament of Ireland was dissolved in 1800.
Henry Grattan described Parnell as "an honest, straightforward, independent man, possessed of considerable ability and much public spirit.
As Chancellor of the Exchequer he was not deficient, and he served his country by his plan to reduce the interest of money. His conduct at the Union did him honour, and proved how warmly he was attached to the interests of his country, and on this account he was dismissed". Parnell married Laetitia Charlotte Brooke in 1774, and together they had four children.