Mary's father, Leonard Horner, and Charles Lyell became friends through their mutual interest in geology, and this was how Mary and Charles met. Charles almost immediately involved her in his scientific research. Their home was often the gathering place for groups of scientists and their wives and families, such as Mary Somerville, Charles and Emma Darwin, and the geologist and palaeontologist, Gideon Mantell and his wife. Mary Lyell was the more sociable in the couple, and she appears to have been able to converse easily with all of these eminent people.
Mary's death in 1873 devastated Charles, and her loss was felt deeply by others too. One American tribute, published in the Boston Daily Advertiser said: 'There are many hearts in the United States which will be saddened by the death of this admirable woman... Her marriage with an eminent man of science gave a scientific turn to her thoughts and studies, and she became to her husband not merely the truest of friends and the most affectionate and sympathising of companions, but a very efficient helper.'