He was known for his pioneering Ornithological Dictionary of 1802, which for the first time accurately defined the status of Britain's birds.

[citation needed] Montagu is best known for his Ornithological Dictionary (1802) and his contributions to early knowledge of British birds.

[2] He was born at the family home of Lackham House in Wiltshire, some three miles south of Chippenham in the northwest of that county, and baptised at Lacock Church on 9 July 1753.

In August 1773 he married Ann Courtenay, niece of John Stuart, 3rd Earl of Bute.

[2] He subsequently entered a relationship with Elizabeth Dorville (daughter of Georg Wolff), who worked with him illustrating several of his scientific articles.