Ulrik Anton Motzfeldt was born on the island St. Thomas, then part of the Danish West Indies.
His father, Peter Motzfeldt (1777–1854) was a noted military officer and father of the Norwegian Constitution who was stationed on St. Thomas from 1802 to 1809,[1] Ulrik's mother, Ernesta Birgitte Margrethe Stenersen (1789–1848), was the daughter of the B. C. Stenersen, stipendiary magistrate of St.
[3] Their daughter Marie Sophie Erneste married jurist and politician Ulrik Fredrik Christian Arneberg.
His most important publications include Den norske Kirkeret (1844) and Lovgivningen om Odelsretten og Aasædesretten (1846).
[6] Motzfeldt was elected to the Norwegian Parliament in 1851, representing the constituency of Smaalenenes Amt (now Østfold).