Johan Lorentz Carstens was born on 13 May 1705 on the island of Saint Thomas in the Danish West Indies.

Margrethe was the daughter of Governor Johan Lorensen, a wealthy man whose financial status benefitted that of Jørgen's via the marriage.

As a result of the marriage, Carstens acquired ownership over two plantations formerly owned by the von Holten family, the Pearl and Crown estates.

Carstens also acquired 400 tønder of land on Saint Croix when Denmark-Norway purchased the island from France in 1733.

[citation needed] Carsten's family moved to Copenhagen in 1739, where they lived in a townhouse in Store Kirkestræde.