After time in other regiments, he was commissioned a Lieutenant Colonel in the Third Argyllshire Fencibles in 1799 and served with them as part of the Gibraltar garrison in 1800 and 1801.

In 1840, he succeeded his elder brother as sixth Earl of Seafield, and sat in the House of Lords as a Scottish representative peer from 1841 until his death in 1853.

[6] Sir William Fraser reported, "In politics his Lordship was a Conservative, and during his long public career loyally supported his party.

"[7] A member of the Church of Scotland, Grant was an ordained elder sitting in the Presbytery of Abernethy, which he also for many years represented in the General Assembly.

Sir William Fraser wrote that:[9]"He was known as the largest planter of trees in Britain... the annals of the Highland and Agricultural Society of Scotland recording that in 1847, that at that date 31,686,482 young trees, Scotch firs, larch, and hardwoods, had been planted under the Earl's direction over an area of 8223 acres.... For these plantations, which were effected in the districts of Cullen, Moray, Strathspey, and Glen Urquhart, the Highland Society awarded to the Earl their gold medal."