He was born at Sukkestad in Toten as a son of district stipendiary magistrate and chancellor councillor David Christian Sommerfelt (1717–1773) and Benedicte "Bente" Christine Hoff.
First he married vicar's daughter Karen Magdalena Mandahl (1764–1791) in March 1784 in Land.
After her death, in May 1793 in Christiania he married stipendiary magistrate's daughter Anna Sophia Hagerup (1775–1821).
He was offered to succeed Gerhard Schøning as professor in these subjects, but instead shifted his academic field again, to practical agriculture and national economy.
In his position, he continued his endeavor for improving practical agriculture, forestry, and other rural enterprise in Christians Amt.