Ponsonby joined the army as a
cornet in January 1800, serving in the
10th Light Dragoons. He was promoted
lieutenant in June 1800 and
Captain on 20 August 1803. He exchanged to the
60th Regiment of Foot in April 1806 and served on the staff of the
Duke of Bedford, then
Lord Lieutenant of Ireland, and briefly for his successor, the
Duke of Richmond. Promoted
major on 25 June 1807, he went into the
23rd Light Dragoons on 6 August 1809 and went with them to serve in the
Peninsular War. He fought well at
Talavera. He was promoted
lieutenant colonel on 15 March 1810, and served as assistant
adjutant-general at
Buçaco and
Barrosa, directing a successful charge by a squadron of the
2nd Regiment of Hussars (
KGL) against the French dragoons. He was given command of the
12th Light Dragoons on 11 June 1811. After the
fall of Badajoz, he distinguished himself in the
battle of Villagarcia (or Llerena) on 11 April 1812, temporarily commanding
Anson's brigade. Ordered by
Sir Stapleton Cotton to detain a superior force of French cavalry under
Charles Lallemand, he successfully delayed them until reinforcements could arrive to flank the French and pursue them into Llerena. He led the 12th Light Dragoons to disperse some of the broken French infantry after the
Battle of Salamanca, and was wounded while covering the withdrawal from
Burgos. At
Vitoria, his regiment was part of the force, under
Sir Thomas Graham, that blocked the French retreat towards
Bayonne. He took part in the
Battle of the Pyrenees and the fighting that followed in the south of France. In Paris at the time of the abdication of
Napoleon as Emperor of the French, he rode through the night to bring the news to
Wellington, who famously, at an inn after defeating the French at the
Battle of Toulouse, snapped his fingers and turned on his heel "in a triumphal pastiche of a flamenco dance." ==Waterloo campaign==