Marcus Pløen Ingstad

Marcus Pløen Ingstad (18 August 1837 – 24 September 1918) was a Norwegian professor of law and legal scholar.

Ingstad was born in Christiania (now Oslo), Norway. He attended the Royal Frederick University (now University of Oslo): cand.philos. (1856), cand.jur. (1861) and Uppsala University: Dr. jur. (1877).

Ingstad was a Professor of Jurisprudence at the Faculty of Law of the Royal Frederick University (1870–1918) and also served as Dean of the Faculty of Law. He was ordained an assessor in the Supreme Court of Norway (1880 and 1891). He was also a legal scholar and was the author of several books on Roman law.

He was married to Dorothea Greve (1839-1927). They were the grandparents of Norwegian explorer Helge Marcus Ingstad.