In 1831 he was created Baron Kenlis, of Kenlis in the County of Meath, in the Peerage of the United Kingdom, which entitled him to an automatic seat in the House of Lords (his other titles being in the Peerage of Ireland).
[2] Lord Headfort first married Olivia, daughter of John Andrew Stevenson, in 1822.
At the time of her early death, of cholera, on 21 July 1834, she left her husband with nine children.
On 6 May 1853, he married Lady Frances Macnaghten, daughter of John Livingstone Martyn and widow of (i) Lieutenant-Colonel James McClintock of the Bombay Army and (ii) Sir William Hay Macnaghten, British Envoy to Afghanistan who was murdered in Kabul in 1841.
Headfort died in December 1870, aged 83, and was succeeded in the marquessate by his son from his first marriage, Thomas.