Promoted to brigadier general at the end of 1805, he was given an important mission to St Petersburg by Napoleon, where he was accompanied by his great friend Claude Testot-Ferry, later a colonel in the cavalry of the Imperial Guard.

On 14 October 1806, while commanding the cavalry of Ney's VI Corps, Colbert served at the Battle of Jena, leading several charges of the 3rd Hussar and 10th Chasseur Regiments against enemy infantry.

"[5] Sent to Spain in 1808 to join the Peninsular War, Colbert fought at the Battle of Medina del Rioseco on 14 July 1808 while serving under Marshal Jean-Baptiste Bessières.

[6] That winter, he commanded the 3rd Hussars and 15th Chasseurs[7] in the cavalry advance guard of Marshal Nicolas Soult, who was pursuing Sir John Moore's British army in its retreat to A Coruña.

Later the same day, however, at the Battle of Cacabelos, Irish Rifleman Thomas Plunket, a noted sharpshooter in the 95th Rifles, one of the British units still under effective military discipline, advanced alone towards the French.