He was Under-Secretary of State for Foreign Affairs to Lord North for a short time in 1783[1] but otherwise was generally very active in opposition.
[1] He was commissioned as a Captain in the Earl of Upper Ossory's Regiment of Bedford Volunteers in 1803, and became its Lieutenant-Colonel.
[1] St John was then nearly 50 and had a long parliamentary career behind him in which he would have been on the opposite side in most cases to Louisa's father.
They lived at Melchbourne Park, Bedfordshire, and had two children, St Andrew and Louisa Barbara (born posthumously) who married Norman Macleod 25th Chief.
Lord St John died at the age of 58, leaving Louisa a widow with a young family.