Vallensbæk Church is supposed to have been erected during the years 1150-1200. At that time it consisted of a Romanesque choir and nave made of chalk ashlars.
The tower was added during the years after 1500 in late Gothic style: The lower part of chalk ashlars and medieval large bricks, the top of medieval large bricks in monk bond only.
The narthex was renovated during a thorough restoration of the church in 1865.
The unique frescos of Vallensbæk Church date back to approx. 1450 and were made by 'Isefjordsmesteren'.