After serving as an engineer (1655–57) in Sweden's Polish campaign, Dahlbergh returned to fight in the war of 1657–58 against Denmark. His diary, which gives a useful account of the war, contains a questionable claim that he played a crucial role in the Swedish victory. After becoming a colonel and quartermaster in 1674, he played an important part in the Swedish war of 1675–79 against Denmark. In the years following, Dahlbergh was responsible for the construction and rebuilding of many fortresses.

In 1693 he was named privy councillor, count, and field marshal as well as governor-general of Bremen-Verden. He became governor-general of Livonia in 1696. Dahlbergh directed the successful defense of Riga against a Saxon attack at the outbreak of the Great Northern War (Northern War, Second) in 1700. He returned to Sweden two years later. He was also an eminent architect and city planner, known for his large, Baroque-style town square in Karlskrona. As a draftsman, he is best known for his illustrations to Suecia Antiqua et Hodierna (“Sweden Ancient and Modern”), which was published posthumously in 1717.