Darre-Jenssen took technical education in Trondhjem, graduating in 1886. He then stayed a few years abroad, returning to Norway to build railway lines. He was titled assistant from 1891, engineer class II from 1895 and engineer class I from 1898 to 1909. During this period he took part in the construction of the Hamar–Sell Line and the Gjøvik Line, as well as the reconstruction of the Drammen Line and Oslo Eastern Station. For the latter project he was chief of construction. He was promoted to chief engineer in 1909. The work with the Drammen Line was not finished until 1922.