Brand was the second son of General Henry Trevor, 21st Baron Dacre, who inherited the barony in 1851, second son of Thomas Brand and Gertrude Roper, 19th Baroness Dacre. His mother was Pyne, daughter of the Very Reverend the Hon. Maurice Crosbie, Dean of Limerick, son of the 1st Lord Brandon (Brandon's wife was a granddaughter of Sir William Petty, FRS). He descended, almost directly, from Colonel John Hampden, "the Patriot"; his forebear, Sir John Trevor III (1624–72) of Plas Teg, son of Sir John Trevor II of Plas Teg and Trevalun, by Anne daughter of Sir Edmund Hampden of Wendover, had married John Hampden's daughter Ruth, who was his first cousin. That is to say the 19th Baron Dacre (aka Gertrude Roper (d.1819) wife to Thomas Brand V (1749–94)) was the great-great-granddaughter of The Patriot.