She was Lady-in-Waiting to HRH Princess Marina, Duchess of Kent From 19 October 1920, her married name became Pratt. As a result of her marriage, Marjorie Minna Jenkins was styled as Countess of Brecknock on 19 October 1920. She gained the rank of Senior Commander in the service of the Auxiliary Territorial Service. She was invested as a Dame Commander, Order of the British Empire (D.B.E.) in 1967 She was invested as a Companion, Most Venerable Order of the Hospital of St. John of Jerusalem (C.St.J.) She was Superintendant-in-Charge, St. John Ambulance Brigade.
In 1938 she Joined the FANY's as a Private (later to be embodied in the ATS). and during the war she served first with motor companies, then with the anti-aircraft artillery, and at the end of the war she was the senior British woman officer at SHAEF in France. Mentioned in dispatches and awarded the Bronze Star (U.S.A.).