His elder brother, Richard Moore, who died unmarried in 1761, represented Clonmel in the Irish Parliament.

His younger brother, William Moore represented Clogher, Clonmel and St Johnstown.

[5] On 3 June 1769, Lord Mount Cashell married Lady Helena Rawdon (1744–1792), second daughter of John Rawdon, 1st Earl of Moira by his first wife Lady Helena Perceval (herself the second daughter of John Perceval, 1st Earl of Egmont).

Their children were:[1] Lord Mount Cashell died in May 1790, aged 59, and was succeeded in the earldom by his son Stephen.

Through his daughter Lady Helena, he was a grandfather of antiquarian Edward King, Viscount Kingsborough.