Soon after marrying the dowager Countess of Pembroke
Mordaunt rejoined the army in 1745 as lieutenant-colonel of the Duke of Kingston’s Horse, one of the temporary regiments raised by noblemen at their own expense during the rebellion. Next year he was turned out of his command to make room for the Duke of Rutland’s son, Lord Robert Sutton, thus losing the prospect of acquiring permanent rank as lieutenant-colonel when the regiment was subsequently placed on the establishment as the Duke of Cumberland’s Dragoons. When the sinecure of clerk of the pipe fell vacant in 1748 he besieged Pelham in London with applications for the place in compensation for the loss of his commission. ‘I am plagued out of my life for this place’, Pelham complained to Newcastle, ‘Jack Mordaunt follows me everywhere ...’ Having failed to extract a promise from Pelham, Mordaunt sent two ‘most pressing letters’ to Newcastle begging for his support. ‘There is one thing’, he wrote, that ‘has given me great pain, that Mr. Levinz [William Levinz, jun.] should have so good a place, who voted against the royal family for three Parliaments together, and this is my third Parliament, and never gave one vote against them’.
