Marius Ormestad (13 December 1874 – 28 May 1964) was a Norwegian trade unionist and civil servant. He was born in Våle, Vestfold. He chaired the Norwegian Union of Iron and Metalworkers from 1898 to 1909, and was manager of Oslo Trygdekasse from 1911 to 1944. He was decorated Knight, First Class of the Order of St. Olav in 1938, and was Knight of the Order of Vasa and of the Order of Dannebrog.