His father Rigby was an MP for Ipswich (1831–37) before Cathcart was born, and his brother Eugene represented two UK constituencies (South Ayrshire and Clackmannanshire and Kinross-shire) at various times between 1885 and 1918.
Cathcart | Earl Cathcart | Charles Cathcart, 7th Earl Cathcart | Rigby Wason | Richard C. Cathcart | Lord Cathcart's | Isaac Cathcart | Frederick Cathcart | Charles W. Cathcart | Charles Cathcart, 8th Lord Cathcart | Charles Cathcart, 2nd Earl Cathcart | Cathcart William Methven | 7th Earl Cathcart |