He was a 1842 graduate of Middlebury College becoming a lawyer. He was the clerk of he Supreme Courts of Addison County, Vermont. He represented Middlebury in the State Legislature from 1860-1862. He was the son of Ira and Betsey Hubell Stewart and husband of Sophia Allen (findagrave.com)
Dugald filled many official positions and was becoming a man of great importance in the State at the time of his death (Severance, B. Frank. Genealogy and biography of the descendants of Walter Stewart of Scotland and of John Stewart who came to America in 1718 and settled in Londonderry, N.H. Greenfield, Mass. : T. Morey & Son, 1905, pg. 145)