Marie Elizabeth Galpin, born de Jongh was the daughter of Lourens de Jongh and his wife Countess Mimi von Schoennberg. Her brother Jim de Jongh was one of the early chairmen of the Johannesburg Stock Exchange. Marie was for some time acting head of the government hospital in Pretoria before she became the first woman teacher in Barberton. By September 1890 she had met E.E. Galpin* and was painting some new flowering plants that he had found in the neighbourhood, so that he could send the paintings with his specimens to Kew Gardens in England. On 23 March 1892 she married Galpin in Pretoria, while her sister Sophia married D.F. Gilfillan*. The Galpins moved to Queenstown, Cape Colony, that same year. They eventually had four sons.
Marie was a tireless walker and fond of outdoor life, and accompanied her husband on most of his plant collecting expeditions. For example, in March 1904 they undertook a collecting expedition to the high mountains bordering Griqualand East and Lesotho, spending about three weeks at an altitude around 3000 m and collecting many mountain species.Her genial nature and knowledge of Afrikaans helped them to make friends and find hospitality wherever they went. She added a number of specimens to his herbarium between 1896 and 1902, some of which she had collected in the neighbourhood of Jeppe's Town, Johannesburg. The heath Erica mariae, which the Galpins discovered in the Riversdale district, was named after her.
Both Marie and her husband became members of the British Association for the Advancement of Science when it held its annual meeting in South Africa in 1905.