Powell had decided to train as a nurse with a view to becoming a missionary in Africa and applied to St. George's Hospital, Hyde Park Corner, London on the advice of her vicar, the Reverend Gliddon.

[3] She then undertook midwifery training at St. George's Hospital, London and in Gloucestershire, attaining her Registered Midwife qualification from the Central Midwives Board in mid-1939.

Her age reportedly "raised eyebrows" among the medical establishment, which deemed her too young for the position, but she proved her critics wrong and would remain there for 22 years.

Powell was part of the government committee that published the Salmon Report on Hospital Nursing, that recommended removal of the title "matron" from the National Health Service in 1968.

[1] Muriel Powell was appointed In the Queen's Honors' list, first, as a Commander of the British Empire (CBE)[5] in 1962 and then as a Dame (DBE)[6] in 1968 for her services to nursing, and specifically her membership of the Salmon Committee and including her tenure as matron of St George's Hospital, London.