In August 1783 Ross was appointed deputy adjutant-general in Scotland, with the rank of lieutenant-colonel, and he served in a similar capacity in India under Lord Cornwallis.
In August 1794 he went with Earl Spencer and Thomas Grenville to Vienna on a special mission to arrange that Lord Cornwallis should command the allies against the French.
He accompanied Lord Cornwallis as major-general to Warley camp in April 1795, and two months later was nominated Surveyor-General of the Ordnance in succession to George Cranfield Berkeley.
He was one of the most intimate friends of Lord Cornwallis, whose correspondence, in three volumes, was edited in 1859 by his son, Charles Ross.
On 15 October 1795 Ross married Isabella Barbara Evelyn, daughter of Sir Robert Gunning, 1st Baronet.