Runciman was homosexual. There is little evidence of a long-term lover but Runciman boasted of a number of casual sexual encounters - telling a friend in later life: "I have the temperament of a harlot, and so am free of emotional complications." Nevertheless Runciman was discreet about his homosexuality, partly perhaps because of religious feelings that homosexuality was "an inarguable offence against God". Runciman also felt that his sexuality had potentially held back his career. Max Mallowan related a conversation where Runciman told him "that he felt his life had been a failure because of his gayness".