Stewart was a career soldier who had served in the Peninsular War as Adjutant General to Allied commander Lord Wellington.

Stewart had returned home from Portugal when he posed for the portrait and was subsequently appointed British Ambassador to Prussia, launching a diplomatic career that saw him play a key role in forming the alliance that defeated Napoleon and attending the Congress of Vienna.

He is shown in hussar uniform, a branch of light cavalry that became prominent during the Napoleonic Wars.

[1] Stewart became a friend and patron of Lawrence, securing him commissions from the Prince Regent from 1814 onwards.

[3] In 1822 Stewart became the Marquess of Londonderry in succession to his brother whom Lawrence had painted several times including his 1809 Portrait of Lord Castlereagh.