There seems at one time to have been an intention that the young student should give up his Indian writership and remain on Lord Wellesley's staff, on the chance of the latter being able to provide for him in the public service in England; but on the advice of Sir John Malcolm, a friend of his father, who went over to Dublin for the purpose of combating the idea, the intention was abandoned, and early in 1824 Montgomery returned to Haileybury, passing through college at the end of that year.
In 1825 he proceeded to India, reaching Madras on 3 November In those days it was the custom for the young civil servants to remain for two years at the presidency town, prosecuting their studies in the native languages.
On the occasion of his retirement he was appointed, at the recommendation of the Marquess of Salisbury, then Secretary of State for India, to be a member of the Privy Council, an honour which is very rarely conferred upon Indian civil servants.
Lord Wellesley had formed a high opinion of him when he worked in Dublin in the lord-lieutenant's private office, and did not fail to exert his influence on his behalf.
By the successive governors under whom he served in the secretariat and in council, the Marquis of Tweeddale, Sir Henry Pottinger, and Lord Harris, he was trusted as a wise and conscientious adviser.
His minutes, when he found himself called upon to dissent from the decisions of the secretary of state or of a majority of the council, were models of independent but courteous criticism.
Indeed, it has been sometimes thought that he carried beyond due limits his advocacy of the claims of his old presidency, as in the case of the Madras harbour project, which was sanctioned by the India office, mainly at his instance, but has been a heavy burden upon the Indian revenues without compensating results.
When the nawáb of the Carnatic died in 1858, Montgomery supported Lord Harris in advocating the extinction of the titular nawábship as a mischievous remnant of a state of things which, for political reasons, it was inexpedient to maintain.
The policy which on this occasion Montgomery opposed had been supported by two successive governors-general, the Marquis of Dalhousie and Earl Canning, but was subsequently reversed.