His mother was his father's cousin, being the eldest daughter of Thomas Browne of Hospital, County Limerick.

After the death of his father in 1720, he succeeded to the family estates which had been under the management of John Asgill because his grandfather Sir Valentine Browne was a supporter of the Jacobite cause who took part in the Battle of Aughrim.

The difficulty experienced in meeting the heavy encumbrances on the impoverished estate fostered disputes in the family and drove close relatives into law with each other, much of which was both protracted and costly.

This refusal caused O'Rahilly to compose a bitter and mournful poem called "Valentin Brown"[5] in which he launches a vitriolic attack on the viscount.

Egan O'Rahilly's poem "Valentin Brown", translated by Frank O'Connor, reads: That my old bitter heart was pierced in this black doom, That foreign devils have made our land a tomb, That the sun that was Munster's glory has gone down Has made me a beggar before you, Valentine Brown