He was the eldest son of General Lord Robert Manners by his wife Mary Digges and succeeded to his father's estate at Bloxholm in Lincolnshire.

[2][8] That regiment was reduced on 24 June 1784,[2] and after a period on half-pay, Manners joined the 3rd Foot Guards as captain-lieutenant on 19 February 1787.

He was considered as a replacement for Sir Henry Peyton, MP for Cambridgeshire, on that gentleman's death in 1789, but unsuccessfully stood at Northampton in the general election in 1790.

[1] In 1791 Manners was promoted to captain of his own company in the 3rd Foot Guards [12] and served with the 1st Battalion of the regiment in the first Flanders campaign.

[7] When war broke out again in 1803, Manners was appointed to the staff of the Eastern District, holding that post until he was promoted to lieutenant-general on 25 September that year.

[2][18] After the establishment of the Regency, he was appointed Clerk Marshal in the King's Household at Windsor on 19 February 1812,[7] and was promoted to full general on 4 June 1813.

A relative of the brothers wrote to the Editor of the Stamford Mercury on 26 March 1841[24] making it very clear that the family knew George wanted Bloxholm to go to Mrs Jenney, writing: for it is the opinion of all who are acquainted with the circumstances, that the testator would never have altered had he been in the full possession of his faculties.