He was survived by his wife Katherine Carpenter and five children from his two marriages. With his first wife, actress Jill Ireland, he had three sons: Paul, who briefly pursued acting; Jason, who tragically passed away from a drug overdose in 1989; and Val, a professional guitarist.
With Katherine, McCallum had two children: son Peter, who fondly remembered him as a kind and loving father, and daughter Sophie, who credits her parents’ support during her recovery from alcoholism as pivotal in her career as a self-help coach. McCallum’s death, attributed to natural causes, occurred at New York Presbyterian Hospital, surrounded by loved ones, and was commemorated by an NCIS tribute episode aired on February 19, 2024, honoring both the actor and his beloved character, Ducky.