After his confirmation, Marstrand initially worked in his uncle's office in Skælskør before apprenticing as a baker in Køge.

[3] Back in Denmark in 1837, Marstrand started working as a clerk for the police master in Helsingør before taking over the family's bakery in Silkegade in 1839.

Under his management, it commenced a large-scale production of rye bread and hardtack and was expanded in 1850 with a steam mill.

When the mill was also destroyed by fire in 1865, Marstrand started a small beer brewery which operated under the name Troels Af.

Marstrand struggled with poor health and had to take long periods off from work after the fire at Vodroff's Mill.