Kerry is the child of Richard Kerry (1915–2000), a Foreign Service Officer and an attorney for the Bureau of United Nations Affairs, and Rosemary Isabel (Forbes) Kerry (1913–2002), a World War II nurse and member of the wealthy Forbes family. Rosemary was born in Paris, France, to American parents. Kerry has three siblings: two sisters, Diana (born in 1947) and Margerie (aka Peggy; born in 1941), and a brother, Cameron Kerry (born in 1950), Cameron Kerry is the General Counsel of the US Department of Commerce.[4] One of Kerry's maternal great-great-grandfathers was Robert Charles Winthrop, the 22nd Speaker of the U.S. House of Representatives. The first governor of Massachusetts Bay Colony John Winthrop is a direct Kerry forbear.[5]

Kerry was raised as a Roman Catholic by his Catholic father and Episcopalian mother.[6] As a child, Kerry served as an altar boy. Although the extended family enjoyed a great fortune, Kerry's parents themselves were upper-middle class; a wealthy great aunt paid for Kerry to attend elite schools in Europe and New England. Kerry spent his summers at the Forbes family estate in Brittany, and there, he enjoyed a more opulent lifestyle than he had previously known in Massachusetts.