Jennings succeeded his father, Sir John Jennings, as head of the family in August 1642, and took residence at Sandridge in Hertfordshire. His mother was Alice, daughter of Sir Richard Spencer of Offley, who bore his father no less than 22 children.
He took the Parliamentary side in the Civil War. He was the father of Sarah Churchill, Duchess of Marlborough, who was the confidant of Queen Anne. He fought for the parliamentary cause in the Civil War, and was captured by the Royalists and imprisoned for some time.
As a moderate he was secluded from parliament under Pride"s Purge in December 1648.
He was re-elected Member of Parliament for Street Albans in Richard Cromwell"s Third Protectorate Parliament in 1659. He took a leading role in the restored Long Parliament during the few weeks of 1660 when the secluded members resumed their seats, and was then elected Member of Parliament for Street Albans for the Convention Parliament.
He was re-elected Member of Parliament for Street Albans in 1661 for the Cavalier Parliament and sat until his death in 1668. Jennings married Frances Thornhurst, daughter and heiress of Sir Gifford Thornhurst, 1st Baronet and Susanna Temple.
She brought with her the manor of Agney, Kent.
Their daughters, Sarah and Frances, were both noteworthy figures at the court of Charles World War II Sarah married John Churchill, the future Duke of Marlborough, in 1677, and was highly influential during the reign of Queen Anne. Abigail Masham, who ultimately supplanted her in the Queen"s confidence, was a first cousin, child of one of Richard"s 21 siblings.
Cavalier Parliament]
He was also elected as Member of Parliament (Member of Parliament) for Street Albans in succession to his father in 1642.
