Tostrup was born at
Hjelmeland in
Rogaland, Norway. He was the son of infantry captain Nicolai Tostrup (1768–1858) and his wife Thale Margrethe Resen Holfeldt (1779–1860). He was one of eight siblings in a family which included goldsmith
Jacob Tostrup (1806–1890) and politician
Hans Tostrup (1799-1856) . In 1828, he was employed by
Haagen Mathiesen (1759–1842) and became manager of Mathiesen's properties in
Hurdal,
Skedsmo and
Trysil. After Mathiesen's death in 1842, he bought the properties in
Hurdal,
Hadeland, and
Nannestad together with Mathiesen's son Mogens Larsen Mathiesen (1799–1875). They then formed the firm
Tostrup & Mathiesen. Mogens Mathiesen's son Haaken C. Mathiesen (1827-1913) soon joined the company, which became one of the largest timber companies in Norway. Tostrup's heirs sold their interest in the Tostrup & Mathiesen company to members of the
Mathiesen family in 1892. It was subsequently renamed
Mathiesen Eidsvold Værk, and much of the company is today continued under the name
Moelven Industrier. ==Personal life==