Ritchie was born in Hatfield, Hertfordshire, the second of two children of Amber (née Parkinson) and Captain John Vivian Ritchie (b. 1928), former Seaforth Highlanders serviceman and advertising executive. John's father was Major Stewart Ritchie, who died in France, in 1940, during World War II. John's mother was Doris Margaretta McLaughlin (b. 1896), daughter of Vivian Guy McLaughlin (b. 1865) and Edith Martineau (b. 1866), the latter by whom he shares close common ancestors with Catherine, Duchess of Cambridge. The McLaughlins have a pedigree going back to King Edward I of England. Both Ritchie's parents remarried to prominent individuals. His father's second marriage was to Shireen Ritchie, Baroness Ritchie of Brompton, a former model and later Conservative politician and life peer. From 1973 until 1980, when they divorced, Ritchie's mother was married to Sir Michael Leighton, 11th Baronet of Loton Park. As a divorcée, she is correctly styled as Amber, Lady Leighton.