His genre was particularly painting working men such as fishermen, shepherds, crofters, pedlars, and farm labourers.
He attended the RSA Life schools and simultaneously was taught by a French artist to paint and draw.
In the Netherlands he was influenced by the painters Anton Mauve (1838–1888) and Jozef Israëls (1824–1911), hence the changing styles of his work.
James Lewis Caw (1864–1950), director of the Scottish National Gallery and the National Portrait Gallery, wrote of McGregor that he probably was the first Scottish genre painter to apply rigorous study of tone in his work and a pleasant if restricted colourist.
Others praised him for the combination of tone with quiet colours and the more subtle light of the Dutch coast.