Part of his early life was spent abroad, and in 1754 he entered the Jesuit novitiate either at St Omer or at Hesdin, but returned to Ireland in the following year when he succeeded to the family estates through the death of his brother in a duel.

[2] In 1766, having conformed to the established religion (Church of Ireland) two years previously, Kirwan was called to the Irish Bar, but in 1768 abandoned practice in favour of scientific pursuits.

During the next nineteen years, he resided chiefly in London, enjoying the society of the scientific men living there and corresponding with many savants on the continent of Europe, as his wide knowledge of languages enabled him to do with ease.

His experiments on the specific gravities and attractive powers of various saline substances formed a substantial contribution to the methods of analytical chemistry and in 1782 gained him the Copley medal from the Royal Society, of which he was elected a fellow in 1780.

His geological work was marred by an implicit belief in the universal deluge and through finding fossils associated with the trap rocks near Portrush that he maintained basalt was of aqueous origin.

There is evidence to suggest that Kirwan was a member of the Society of the United Irishmen,[5] a revolutionary republican organisation in 18th century Ireland.

The United Irishmen were founded as a reformist club by a group of Irish radical Protestants and Presbyterians in 1791, influenced by the American and French revolutions.

At the time of the Union, Kirwan refused a baronetcy, died in Dublin in June 1812, and was buried there in St. George's Church, Lower Temple Street.