Cumming was born on 27 January 1965 in Aberfeldy, Perthshire, Scotland. He studied at Royal Scottish Academy of Music and Drama. Cumming is openly bisexual. He was married to Hilary Lyon from 1985 until they divorced in 1993. He had been in a civil partnership with Grant Shaffer since 2007. Cumming gained American citizenship in 2008; he has been a dual British-American citizen since then.