In 1791, as a lieutenant, he served with Prince Edward Augustus, Duke of Kent and Strathearn, the fourth son of George III, in Gibraltar.

He would serve on the prince's staff in Gibraltar, Quebec, the West Indies, and Nova Scotia for twelve years.

In 1798, he was promoted to major, and the following year, was the senior aide-de-camp and acting quartermaster general for the Duke of Kent when he became Commander-in-Chief, North America.

While he was Commander-in-Chief, his wife Amelia Ann Smyth (née Cantelo) died and has a memorial to her in St. Paul's Church (Halifax, Nova Scotia).

There is a memorial to him in the church of All Saints, Chelsworth, Suffolk, England that was erected by his brother John Gee Smyth, Rector of Chelsworth, Suffolk and Chaplain to the Prince Edward, Duke of Kent and Strathearn.