Manners was first cousin to Sir William Manners, Bt., who in 1806 succeeded in obtaining one seat for Grantham by compromise and prodded him into it. His father had been colonel of the 26th Light Dragoons and after his death he hoped the Duke of York, as commander-in-chief, would provide for him. In the summer of 1806 he had the duke’s mistress Mary Anne Clarke’s assurance that ‘she would endeavour to get a place for him’ and had seen a letter to prove it, in which the duke ‘said that he would give Mr Manners a place suitable to his name and family’. Manners also had a claim on account of a regimental debt due to his father, on the strength of which he had obtained advances of money from his wife’s brother-in-law Rowland Maltby, to whom he assigned the debt for the purposes of repayment.
Convenient as it may have been to him to be in Parliament, Manners, whose patron professed support for the Grenville ministry, made no mark there. He was described as ‘a sportsman’ and his wife as ‘a celebrated beauty’.