Serving Christian IV, Holk was commander of the Danish-Scottish force in the Battle of Stralsund in 1628, defending the besieged town of Stralsund against Wallenstein's imperial army. When Christian was forced into a peace with Wallenstein in 1629, Holk entered the latter's service. In 1632, he was given a cavalry command. His unit, referred to as "Holk's Horse", was known for their fierce attitude not only in battle, but also in pillage and rape - "notorious even in an age of atrocities". He took part in the devastation and looting of the Electorate of Saxony, and faced Gustavus Adolphus of Sweden's cavalry in the Battle of Lützen. The battle marked the end of his active career, though he remained in office as a senior commander. The following year, he died of plague.
After the appearance of Grantville altered the course of the Thirty Years' War and forestalled the Battle of Lützen, Heinrich Holk entered into the service of Albrecht von Wallenstein when the latter seized power in Bohemia. However, Holk grew dissatisfied with the arrangment, and betrayed Wallenstein by attempting to plunder Prague when Wallenstein led his army out to confront the Austrians at the Second battle of the White Mountain.
Holk's plan was foiled by an alliance of up-timers and Prague's large Jewish community, which was led by Morris Roth. Upon hearing that a victorious Wallenstein was on his way back to Prague, Holk immediately fled north to Saxony, where he had offered the services of his army to the Saxon Elector, John George.
However, when war came between the USE and Saxony in 1635, Holk realized once again that he'd selected the wrong employer. When the Saxon cause was clearly lost, Holk abandoned John George, and sought employment elsewhere. The mercenaries in his employ had plundered Saxony before the war began, and were found and slaughtered without mercy by Georg Kresse and his followers.