He was born at Vinger in Hedmark, Norway. He graduated in 1871 with a law degree. Engelhart was a public prosecutor by profession. He was a senior prosecutor at Kongsvinger from 1873. From 1876 he was the Supreme Court Attorney at Vinger, where he also was the mayor between 1881 and 1889.
He was Minister of Auditing 1891–1892, member of the Council of State Division in Stockholm 1892-1893 and 1897–1898, and Minister of the Interior 1895–1897. He served as bailiff (amtmann) in Bratsberg amt (now Telemark) in 1898 and Jarlsberg og Larviks amt (now Vestfold) in 1902.
His son Bernt (1889–1961) was a veterinarian, and married schoolteacher Alette Nicolaysen who became a national housewives' leader. His daughter Engelke (1885–1973) married ship-owner Wilhelm Wilhelmsen.
- Knut Dørum. "Thomas von Westen Engelhart". Store norske leksikon. Retrieved January 1, 2018.
- "Register of Persons "Norway's Governments since 1814"". Government.no. Retrieved 2011-05-11.
- "Johannes Steen's First Government". Government.no. Retrieved 2011-05-11.
- Haavardsholm, Espen. "Alette Engelhart". In Helle, Knut (ed.). Norsk biografisk leksikon (in Norwegian). Oslo: Kunnskapsforlaget. Retrieved 24 February 2013.
- Kolltveit, Bård. "Wilhelm Wilhelmsen". In Helle, Knut (ed.). Norsk biografisk leksikon (in Norwegian). Oslo: Kunnskapsforlaget. Retrieved 24 February 2013.