A nurse and senior army officer in the Second World War, Kathleen Best was born at Summer Hill in Sydney on 28 August 1910. Best was educated in Sydney and undertook nursing training at Western Suburbs Hospital and midwifery training in the Crown Street Women's Hospital. Having completed her training, Best nursed at Wyong Hospital on the New South Wales central coast, was appointed Acting Matron at the Rachel Forster Hospital in Sydney and later Deputy-Matron at the Masonic Hospital in Ashfield.

Best's military nursing career began with her appointment to the Australian Army Nursing Service on 30 May 1940. She was posted as Matron to the 2/5th Australian General Hospital and embarked for the Middle East in October that year. After opening in Palestine in December 1940, the hospital moved to Greece in April 1941. During the short-lived campaign, Best - the senior matron in Greece - and her colleagues endured regular German air raids. Best and 39 colleagues volunteered to remain in Greece after the evacuation knowing that they risked captivity. Within hours of deciding to stay, however, they too were ordered to leave, the last Australian nurses to do so. They survived further German air attacks on their ship before reaching Crete and later Alexandria. Best was awarded the Royal Red Cross for her service in the Greek campaign.

The 2/5th Australian General Hospital was then re-established in Palestine and reorganised under Best's supervision, but in August 1941 moved again, this time to Eritrea on the African coast. By March 1942 Best had returned to Australia, where her appointment to the AIF was terminated in mid-June. This, however, was not the end of her contribution to Australia's war effort. A month after leaving the AIF she became the Controller of full-time Voluntary Aid Detachments, which in September became part of the Australian Army Medical Women's Service. She held this post for seven months until she received a promotion to lieutenant colonel in February 1943 and was posted as Assistant Adjutant General (Women's Services). In September 1944, it having become clear the Allies would eventually prevail, she became Assistant Director of Women's Re-establishment and Training for the Department of Postwar Reconstruction. Among her responsibilities was the task of assisting servicewomen and female war-workers to adjust to civilian life once the war ended.

On 12 February 1951, Best became the founding Director of the Australian Women's Army Corps, which was shortly after given the designation "Royal". In September 1952 she reached the rank of honorary colonel and four years later, in 1956, appointed Officer of the Order of the British Empire. Despite her achievements Best has been described as a modest woman with an engaging sense of humour. Those who served under her considered Best an inspiring leader who ruled with a firm hand, but who also treated her subordinates with fairness. Aged only 47, Best became ill with melanomatosis and died on 15 November 1957 at Epworth Hospital in Richmond, Melbourne.