Sir Ralph Milbanke was the second son of Sir Mark Milbanke, 2nd Bt. and his wife Jane, only daughter of Sir Ralph Carr of Cocken, Co. Durham. He succeeded his elder brother, Mark Milbanke, 3rd Bt. when the latter died, unmarried, in 1705. He married firstly Elizabeth D'Arcy (d. 1720) eldest sister of Robert Earl of Holdernesse, and secondly Anne, daughter of Edward Delavel of South Dissington, Northumberland, portrayed here. He was succeeded by his son Ralph, eldest son of his second marriage.