He was with his father on his flight to
Brabant in February 1721. On 10 June 1727, following his return to England, he married
Henrietta St John (15 July 1699 – 26 March 1756), daughter of
Henry St John, 1st Viscount St John, of
Lydiard Park, Swindon, by his second wife Angelica Pelissary, daughter of Georges Pelissary, treasurer of the navy to King Louis XIV. Henrietta was thus half-sister of the highly influential
Henry St John, 1st Viscount Bolingbroke, the son of her father's first marriage. In 1730 he purchased
Barrells Hall, Ullenhall, Warwickshire, the ancestral home of the Knight family, from his second cousin Raleigh Knight. He entered parliament in 1734 as 2nd M.P. for the borough of
Great Grimsby, and was at first identified with the Bolingbroke interest. John Page, MP for Grimsby in 1727, wrote in 1762 concerning Knight that his interest in Grimsby: "… was stronger there than any man's because they have had more of his money than anybody's and he has always been punctual to all his engagements with them and they with him". On the break-up of his marriage before 1736 and following Bolingbroke's return to France, he became less partisan, but held his seat until 1741. In 1740, on the death of Sir Joseph Eyles, Robert Knight snr. had repurchased Luxborough House, to which his son succeeded in 1744. On 8 August 1745 he was created
Baron Luxborough, of Shannon, in the peerage of Ireland. In 1747 he won the seat, as 1st member, of
Castle Rising, Norfolk, which he retained until 1754. In 1749, he sold the estate at Luxborough to a London merchant named James Crokatt, who was in the Carolina trade. He became Agent for the Province. He was instrumental in obtaining the Royal Charter for the incorporation of the Charleston Library Society in 1755. whose heirs sold it to Sir
Edward Walpole, K.B. (d.1784), younger son of the Prime Minister Sir
Robert Walpole. In March 1761 he obtained the position of
Recorder of Grimsby. In the general election of 1761 Luxborough procured the return of his son Henry as MP for
Great Grimsby, as 1st member. On the sudden death of his son in August 1762, Luxborough decided to stand himself in the resultant by-election, and was returned unopposed, holding the seat until 1768. He explained his decision to stand thus: "As money can be no consideration in my unhappy situation and as possibly hereafter it may be an amusement to be in Parliament". He gave support to the
Earl of Bute, Prime Minister between 1762-63. On 14 May 1763 he was further raised in the Irish peerage by Bute's successor
George Grenville, Prime Minister between 1763–65, becoming
Viscount Barrells of Co. Catherlough and
Earl of Catherlough. In 1770 he stood successfully as 2nd member in the by-election for
Milborne Port, Somerset, which seat he held until his death on 30 March 1772, aged 69. He was created
Knight of the Bath (KB) 18 May 1770. ==First marriage==