Promoted again to major-general he served on the staff in eastern England before being posted to act as Lieutenant Governor of Upper Canada from 1799 to 1802.
At the following general election of 1806 he fought a duel with the winning candidate, John Wharton, a fellow officer, which ended his political career.
A man who lived beyond his means he was forced to sell most of his own and his wife's inheritance to pay his debts but nevertheless spent time in prison in 1812 for owing money.
Their eldest daughter married firstly Major-General John Clitherow and secondly Henry Peters of Betchworth Castle.
The Municipality of Napierville (which formed on the lands of the Seignory of Léry) in Quebec, Canada, is named after him.