During a lifetime interest in local history Matthew Mackey built up a unique collection of locally printed works. Virtually all the material relating to the North East of England was obtained as a result of purchase from his executors in 1919 (131 tracts) and from the public sale of the rest of his library in 1920. In total some 200 volumes were added to stock with the original 131 tracts being published before 1700. These locally printed Civil War Tracts relating to the activities of the Scottish army between 1640 and 1650 are the most significant items in the collection.
Matthew Mackey, who succeeded his father in the family leather business, also inherited the family interest in local antiquities and achieved for himself a considerable reputation as a book collector with a particular interest in the works of the Newcastle book illustrator Thomas Bewick. Mackey was a member of the Newcastle Free Libraries Committee (1911–1913) and acted as the Honorary Librarian of the Newcastle Society of Antiquaries from 1894–1899.
He died at home in Jesmond and was buried in St Andrew’s Cemetery on Friday 2nd May 1913. His exact age is not known but he was thought to be approximately 60 years of age.