Mary travelled to England, arriving in September 1854. She heard the news of the Crimean campaign and wanted to help the troops she had known in Jamaica. Despite being rejected as a hospital nurse for the British Military Hospitals, she was determined to go. She sent notices announcing her departure on 25th January 1855. In her autobiography she describes stopping en route to the Crimea to visit the military hospital at Scutari and take in provisions. She had many joyful reunions with soldiers she had known years earlier in Jamaica.

According to Mary she also met Florence Nightingale "A slight figure, in the nurses’ dress; with a pale, gentle and withal firm face, resting lightly in the palm of one white hand, while the other supports the elbow - a position which gives to her countenance a keen inquiring expression, which is rather marked."

Mary was often in attendance at the sick wharf, feeding and tending to the wounded soldiers as they prepared to embark for Scutari. Mary set up the British Hotel with her business partner Mr. Day two miles from Balaclava. As well as selling everything from shoes to tooth powder, Mary also rode out to deliver supplies of food and drink to the troops during the siege of Sevastopol and helped with the wounded after the final assault. She was affectionately known by the troops as 'Mother Seacole.'

She stayed in Balaclava for as long as the troops were there and returned to England in 1856.