James Grant Forbes (October 22, 1879 - April 24, 1955) was born in Shanghai, China, where the Forbes family of Boston amassed a fortune from the opium trade and merchant banking after the Opium Wars. He went to school in England and graduated from Harvard University. Forbes was a successful international lawyer and banker. He married Margaret Tyndal Winthrop, who came from a family with deep roots in Massachusetts history going back to the John Winthrop, the first governor of the Massachusetts Bay Colony. The couple lived in the United States for the early years of their marriage, but after the birth of their third child they moved to Europe and made Paris, France their home. During World War I, and after having had several more children, they moved to England, where they rented Barrow Green Court . Margaret had two English governesses to help bring up her 13 children.

Forbes is the father of Rosemary Forbes Kerry and the maternal grandfather of 2004 U.S. Presidential candidate Democrat John Kerry and of the 1991 French Presidential candidate Green Brice Lalonde.