In 1866, Lecointe took command of the 2nd Grenadier Regiment of the Imperial Guard Corps. With the outbreak of the Franco-Prussian War in July 1870, he led the regiment as part of the Army of the Rhine. He was wounded during the Battle of Mars-la-Tour on 16 August 1870 and was surrounded in Metz with the rest of the Army of the Rhine on 19 August 1870, beginning the 70-day Siege of Metz.