A general's son, he was an officer in the German army until 1912, when he left to pursue his writing career.

Two of his earliest important works, the play Offiziere ("Officers"; 1911) and the poem Vor der Entscheidung ("Before the Decision"; 1914) established his anti-war beliefs and his belief that the social order must be based not on authority, but on the integrity and responsibility of the individual towards humanity.

Unruh's works were anti-militaristic and called for world peace and brotherhood.

Some of his more notable works include Der Opfergang ("Way of Sacrifice"), a powerful anti-war piece written during the siege of Verdun and published in 1919, Ein Geschlecht ("A Family"; 1916) and its sequel Platz (1920), and Heinrich von Andernach (1925).

He finally returned to Germany in 1962 and died in the town of Dietz at age 85.