Ross was present at the Siege of Ciudad Rodrigo in January 1812, the Siege of Badajoz in April 1812 and at the Battle of Salamanca in July 1812. After the Battle of Vitoria in June 1813, Ross's guns were continually with the most advanced troops, and they captured the sole remaining piece of artillery held by the French troops. He was rewarded with promotion to lieutenant colonel on 3 July 1813. In July 1813, Ross also took part in the Battle of the Pyrenees, which was followed by actions at Bidassoa in October 1813 and Nivelle in November 1813. During the Battle of the Nive in December 1813, Ross had his horse shot out from under him, but he was unharmed and in April 1814 he fought at the Battle of Bayonne. Following these military successes, he was appointed a Knight Commander of the Order of the Bath on 4 January 1815. During the Hundred Days, Ross was engaged at the Battle of Waterloo in June 1815, and although half his guns were disabled, the remainder took part in the pursuit of the French. He was awarded the Russian Order of St. Anna, 2nd Class on 8 October 1815.