He was most likely an apprentice in Abraham Kløcker's trading house where he is known to have worked for a couple of years and whose step-daughter he married in 1723.
From 1729 to 1740, Blach, Jacob Severin and Rasmus Sternberg held a monopoly on trade on Northern Norway (then known as Finmarken).
In 1763 he was appointed to managing director of the General Trade Company (Det almindelige handelskompagni).
His trading company was passed on to his son Christian Schaarup Blach.
[1] Blach married Kløcker's step-daughter Birgitte Mangor (1699 – 17 January 1778) in the Church of Holmen on 17 November 1723.