From his father's third marriage, he had a younger half-sister, Lady Essex Montagu (wife of Henry Ingram, 1st Viscount of Irvine).

In 1666 and 1667, Montagu was a captain of the Duke of Monmouth's Horse in the eastern counties while the Dutch were on the coast.

[3][2] Montagu inherited the title of Earl of Manchester on the death of his father in 1671 and took on the posts of Lord Lieutenant of Huntingdonshire and Custos Rotulorum.

[2] In October 1681 Lord Manchester decided to go abroad because he had become too closely involved with cabalistic men in Northamptonshire.

Anne was the only daughter of Sir Christopher Yelverton, 1st Baronet of Easton Maudit in Northamptonshire and Anne Twisden (youngest daughter of Sir Thomas Twisden, 1st Baronet of Roydon Hall).

[3] Together, Anne and Robert were the parents of five sons and four daughters, including:[1] He died at Montpellier in France at the age of about 48 and was buried at Kimbolton.