In 1920, Mayer became Chief Curator at the Bavarian State Paintings Collection (Alte Pinakothek) and as Associate Professor at the University of Munich.
[1] A disciple of the Swiss Heinrich Wölfflin (1864–1945), an eminent representative of the formalist movement, Mayer was the first to apply a modern methodology to the study of the history of Spanish art.
As was the case for Jews in Germany, he was subjected to financial fines and confiscatory taxes, his home in Tutzing was confiscated and he was forced to sell personal property, including works of art.
The notorious Nazi SS art looter Bruno Lohse was investigated for his role in Mayer's death.
[6] In 2014 France decided to restitute a painting the Nazis stole in 1943 to his daughter, Angelika Mayer, who was 84 years old at the time.
[5][7] In 2020 an agreement was reached between the Diamond estate and the Mayer heirs concerning Jacopo di Cione, Madonna Nursing the Christ Child with Saints Lawrence and Margaret; Predella: the Man of Sorrows, Mater Dolorosa, and Saint John the Evangelist, with two coats of arms,(14th century)[8] Mayer also owned the 16th-century painting Still Life with Game Fowl by Juan Sánchez Cotán, and is thought to have sold it through the Munich auction house of Hugo Helbing on 24–25 November 1933.