M B Thomas (as she was known) was educated at King Edward VI High School, Birmingham and read Natural Sciences at Newnham College 1894-98 (MA 1936). She was a Demonstrator in Chemistry at Royal Holloway College and came to Girton in fill the same position in 1902. She was appointed as Director of Studies in Natural Sciences in 1906 and stayed at Girton until she retired in 1935. She taught over 300 students in the Girton laboratories, known as 'Tommy Labs' and was renowned for her rigorous training in accuracy and technique. The Girton labs closed on her retirement.