He was the son of a Munich stone sculptor. After he acquired his first training in his fathers studio, he studied at the 'Münchener Kunstgewerbeschule' under professors Wadere and Berndt. In 1906 he assisted sculptor Wilhelm von Rümann with the creation of the two marble lions of the Feldherrnhalle; in 1911 he helped sculptor Hubert Netzer when he created the Jonasbrunnen in Munich. In 1913 he went to the Munich Art Academy, where he was a Meisterschüler of Professor Herman Hahn. Mayer-Fassold’s studies were interrupted by the war, during which he served in the military, but continued in 1919. A year later he won two first prizes for his sculpture 'Trade and Industry' which was placed at the Reichenbach Bridge in Munich. Within two years he was awarded several other prizes, including a first prize for his war memorial for the Bavarian Army Museum in Munich ('Denkmal des bayerisches Heeres im Armeemuseum'), a second prize for his 'Kruzifixwettbewerb' in Windsbach', a first prize for the 'Lenbachbrunnen' in Schrobenhausen, and a second prize for the 'Gedächtnistafel' am Rathaus zu Weiden.
The works of Mayer-Fassold, who worked in stone, wood, bronze and terracotta, were often inspired by mythological motifs. His style of logical and clear forms was a continuation of the style of Adolf von Hildebrand.
Mayer-Fassold, who was a member of the Münchener Secession, displayed his works for the first time in the Glaspalast in 1919; in 1920 he was already represented with six works in the Glaspalast. Two decades of exhibitions of his works at the Great Munich Art Exhibitions would follow; his sculptures were also displayed at exhibitions in Cologne, Düsseldorf, Berlin and Rome. In 1924 Mayer Fassold displayed his bronze 'Due ragazze' ('Two Girls') at the XIV Biennale in Venice.
In 1927 he created several stucco reliefs for the Parkhotel Mannheim; one of them was depicted on the cover of 'Die Kunst für alle', 1927/1928 (see above). In 1929 Mayer-Fassold created the 'Fischerbrunnen' at the Nikolaiplatz in Munich. In the same city he also created sculptures for the Darmstädter Bank and the Landesfuttermittelstelle, as well as 9 reliefs for the Bauzunfthaus and the figure 'Mädchen mit Krug' for the Städtische Gallerie.
In 1933 Mayer-Fassold took with 3 works part in the exhbition 'Staatliche Kunst-Ausstellung München, 1933, Neue Pinakothek. After 1933 he was increasingly commissioned to create sculptures for military facilities; for example, for the barrack in Straubling he created a stone relief ('Barbara') and a Third Reich eagle. In 1937, for the occasion of the opening of the first Great German Art Exhibition, he created a mythological figure which was placed in the Ludwigstrasse. In the same year, for Benito Mussolini’s visit to Munich, Mayer-Fassold created the 4-metre-high 'Fackelträger' ('Torch bearer'), which was placed in front of the entrance of the Hofgarten. In 1940 he displayed 'Mädchen kämmend‘ (English Zement) at the 'Herbst-Ausstellung‘ of the Preussische Akademie der Künste’, Berlin. A year later Mayer-Fassold took part in the Berlin exhibition 'Kunst Ausstellung, Hilfswerk für deutsche bildende Kunst in der NS-Volkswohlfahrt, and in the same year also in the 'Münchner Kunstausstellung Danzig'. In 1942 he studied as official guest at the Deutsche Kunstakademie in Rome.
From 1938 to 1943 Mayer-Fassold was represented -with an average of 3 works per year- at the 'Ausstellung Münchener Künstler' in the Maximilianeum. At the Great German Art Exhibitions, Mayer-Fassold was represented with 13 works; the most famous was his 1942 sculpture 'Gott des Lichtes' ('God of the Light'). Several of his works were depicted in 'Die Kunst im Deutschen Reich'.
Eugen Mayer-Fassold died in 1973 in Munich.