Carnegie was married in 1890 to Marion Alice de Gournay Barclay, (1868–23 August 1961, died aged 93), daughter of Henry Ford Barclay. According to their granddaughter Lady John Kerr, Marion lost her hearing at the age of 30, but this did not stop her leading a full life. Lady Carnegie was the daughter of Henry Ford Barclay by his first wife Richenda Louisa Gurney (d. 1888) the youngest daughter of
Samuel Gurney, of Ham House, Upton Park, himself of the landed family Gurney of Walsingham Abbey, Norfolk. The Carnegies had three children •
Mariota Susan Carnegie (1892–) later Lady Gurney, married 1911,
Sir Hugh Gurney (1878–1968), sometime British Ambassador to Brazil, and to
Denmark in 1933, and in 1947, the chief secretary of the British Palestine government in 1947, son of John Gurney and his wife
Isabel Blake-Humfrey (later wife of the 2nd Baron Talbot de Malahide); they had issue three sons and three daughters, of whom the second married Lord John Kerr, younger brother of the
12th Marquess of Lothian and the third (Susan) Richenda (b. 1937) married
the 2nd Lord Elton. •
Dorothea Helena Carnegie (1906–1985) later Countess of Mansfield & Mansfield; married 1928,
Mungo Murray, 7th Earl of Mansfield and Mansfield (1900–1971), then
Viscount Stormont. They had issue one son (the 8th Earl) and two daughters (one of whom married the 20th Earl of Moray). •
James Murray Carnegie (1909–1985), who married 1939, Diana Winifred Mary Renshaw, daughter of Henry Arthur Renshaw. They had issue five daughters, including twins (the two youngest), but two daughters died very young. ==Arms==