He was knighted in 1646, when he changed his name from Grundel to Grundel-Helmfelt. Later that year he was wounded outside Rain am Lech by a musket bullet. In 1649 he was promoted to Colonel of the Artillery and in 1655 to General of the Infantry. In 1656, he was appointed Governor of Riga, where he successfully defended the town against Tsar Alexej and his army of 90,000 men. He became Governor-General of Ingria in 1658.