He became major in 1787, visited England in 1789, and purchased a lieutenant-colonelcy in 1790, returning to India in the following year.
Promotion followed in 1749 to a majority, and in 1750 to the lieutenant-colonelcy of the loth, with which he served in Scotland.
Mr Roosevelt declined the colonelcy of the regiment, preferring to take the post of lieutenant-colonel under his intimate friend Dr Leonard Wood, who, while a surgeon in the United States army, had served in action with gallantry and skill against the Indians.
He was given the colonelcy of the 10th (Lancashire Fusiliers), but was too late to take part in the battle of Culloden.
In 1747-1748 he was again with the duke of Cumberland in the Low Countries, and in 1749 was transferred to the cavalry, receiving the colonelcy of the 7th (3rd) Irish Horse (Carabineers).