Christensen was born into a West Jutland peasant family and starting as a herd boy, he was educated a teacher and joined politics at an early age.

In the first Left cabinet of J. H. Deuntzer, Christensen was Minister of Cultus and the strongman of the government, introducing reforms in the village school system.

During this period he introduced female suffrage in local politics and tried to solve the problem of the defense.

In addition, a law was passed in April 1907 that authorised state contributions for unemployment relief.

The Alberti scandal in 1908 led to his fall and weakened his position, but he was still the leader of his party participating in the second Carl Theodor Zahle cabinet 1916–1918.