Rosamund Powell was born in Reading. After leaving school she became an active member of the Labour Party League of Youth. Other branch members included John Boulting, Josh Francis and Roy Poole. Powell, like most members of the LPLY, was to the left of the leadership of the Labour Party. This resulted in them having close contact with the Reading Branch of the Young Communist League, that included William Ball, Thora Silverthorne and Reginald Saxton.
On the outbreak of the Spanish Civil War it was decided to form a Spanish Medical Aid Committee. In his autobiography, All My Sins Remembered (1964), Peter Spencer, 2nd Viscount Churchill, explained what happened: "A group of us - three well-known medical men, a famous scientist, several trade unionists, and one communist - formed a committee for the purpose of collecting money for medical supplies to be sent to the Spanish Government forces."
Powell and her friends, Roy Poole, John Boulting, Thora Silverthorne and Reginald Saxtondecided to volunteer to join this group, whereas Josh Francis and William Ball joined the International Brigades.
The First British Hospital was established by Kenneth Sinclair Loutit at Grañén near Huesca on the Aragon front. Other doctors, nurses and ambulance drivers at the hospital included Reginald Saxton, Alex Tudor-Hart, Archie Cochrane, Penny Phelps, Rosaleen Ross, Aileen Palmer, Peter Spencer, Patience Darton, Annie Murray, Julian Bell, John Boulting, Rosamund Powell, Richard Rees, Nan Green, Lillian Urmston, Thora Silverthorne and Agnes Hodgson.
Powell herself became worked for the Spanish Medical Aid Committee as an administrator in Barcelona. She remained in Spain until 1938. On her return to Reading she married Roy Poole, who had worked as an a with the British Medical Aid Unit.