doneraile was the son of hayes st leger, 3rd viscount doneraile and lady charlotte esther bernard. he married mary ann grace louisa lenox-conyngham, the daughter of george lenox-conyngham and elizabeth holmes, on 20 august 1851. together they had two daughters and a son, although only his daughter emily ursula clare st leger survived to adulthood. he sat in the british house of lords as an irish representative peer between 1855 and 1887, having succeeded to his father's title in 1854. he held the office of deputy lieutenant and gained the rank of honorary colonel in the service of the 9th battalion, king's royal rifle corps.