In 1749 Bachmann entered French service as a cadet. He was soon promoted to Ensign in the company of his father and in 1750 was promoted to Captain of the Grenadiers of the same regiment. In 1756 he became commander of two companies of the Regiment. In 1762 he was promoted to Major of the Regiment Waldner von Freudenstein. During this period he fought in various engagements of the Seven Years' War. In 1764 Bachmann became Lieutenant Colonel and was transferred to the Regiment of the Swiss Guard, where he kept his rank though officially he was Major of the Regiment. In 1768 he obtained the rank of Brigadier and in 1780 that of Marechal de Camp, while still serving as Major of the Swiss Guards. In 1778 Bachmann received the Royal and Military Order of Saint Louis. In 1792 he became also the owner of a company of the Swiss Guard Regiment.
Death
Major Bachmann was in direct charge of the 900 Swiss Guards present during the 10 August Insurrection, when revolutionaries stormed the palace of the Tuileries. The nominal commander of the Guard, the elderly Colonel d'Affrey, was in poor health and had delegated Bachmann to bring the regiment into central Paris during the evening of 9 August. Having deployed his Swiss to defend the palace Major Bachmann escorted King Louis XVI and the Royal Family to the National Assembly where they sought refuge. About 650 Swiss Guards were killed, either during the fighting which broke out spontaneously shortly afterwards, or after surrender. Arrested by the revolutionaries Major Bachmann was accused of treason for ordering the Swiss Guard to resist the storming of the royal palace and thereby offending the "Majesty of the People". Bachmann refused to acknowledge the tribunal which was trying him, as the Swiss soldiers in French service were entitled to be tried by their own courts. His trial was interrupted in the late afternoon of 2 September 1792 when the September Massacres of hundreds of political prisoners took place at the Conciergerie and Abbaye prisons. A lynch mob invaded the courtroom where Major Bachmann and other Swiss Guards were being tried before the official Tribunal of 17 August. The crowd retreated when ordered to clear the room by the presiding judges and Bachmann "passed through their shambles unharmed on his way to the scaffold". Bachmann was then sentenced to death, and guillotined on 3 September 1792. He stepped onto the scaffold still wearing the red uniform of the Swiss Guard and his countenance struck those who watched so much that he was remembered by the French poetLamartine in one of his works
Bachmann's name is also engraved on the monument of the Dying Lion in Lucerne, by Bertel Thorvaldsen, where he figures as second on the list of the fallen.
