Dr Reginald Crawley, Matthew's father, was mentioned twice in Series 1. He died between 1909 and 1912 and was a doctor in Manchester until his death. As he predeceased his cousins James and Patrick Crawley, his son Matthew became heir to the Earldom of Grantham until his own untimely death. Reginald's great-grandfather was a younger son of the 3rd Earl of Grantham.

He studied medicine with his brother-in-law under the tutelage of his father-in-law. Dr Clarkson admitted in 1912 that he was familiar with Reginald's work on the symptoms of infection in children. He also treated dropsy of the heart, a process witnessed by his wife, who later encouraged Dr Clarkson to use the same treatment for John Drake despite Violet's protests.

Isobel later described to Mary and Tom how "sick" with love she was when she got engaged to Reginald. When they described their own romances with Sybil and Matthew respectively, Isobel remarked "Aren't we the lucky ones?!"

Murray: "His mother is alive and he lives with her. His father, obviously, is not. He was a doctor."
Robert: "I know. It does seem odd that my third cousin should be a doctor."
Murray: "There are worse professions."
— Murray and Robert discussing the new heir Matthew[src]