Beginning in the 1940s, Lortz made his ecumenical views available to general readers as well as to scholars in order to promote reconciliation between Catholics and Protestants.
His writings played a role in the thinking that manifested itself in the Second Vatican Council's Decree on Ecumenism, Unitatis Redintegratio (21 November 1964).
From 1913 to 1923 he lived in Bonn, where the church and Reformation historians Heinrich Schrörs and Joseph Greving [de] influenced his further intellectual development.
After the Nazi seizure of power in 1933, he published a treatise on the "Catholic accommodation with National Socialism" (Katholischer Zugang zum Nationalsozialismus).
But he lost his position at the University of Munster after the post was returned to Georg Schreiber whom Lortz had replaced by the order of the Nazi authorities.
Among Lortz's better known students are Manns, Erwin Iserloh [de], Karl Pellens, Armin Lindauer, and Alex Schröer.