He was born in Flekkefjord as a son of merchant and sawmill owner Nils Henriksen Beer (1690–1746) and his wife Anna M. C.
[1] His father acquired burghership in 1736, and was probably a part of the first generation of the family to be born in Norway—Jens Henrik Beer's grandfather probably immigrated from Germany or the Netherlands.
[2] Beer was married twice; first to Elisabeth K. J. Eide (1736–1767) from 1763 to 1765, then to Ellen Bolette Færø (1745–1817) from 1769 to his death.
During the Seven Years' War he saved Scottish cargo by sailing under a Danish flag, and even sold it in France.
In Norway, to which he gradually retreated, he was a ship-owner and owned sawmills at Tjørsvaag, Fjeldså and Sirnes in the Flekkefjord district, at Haukom in Siredalen and at Feda.