In 1927 he was appointed professor with chair at the University of Rostock, where he headed the Institute of Art History until 1939 and was Dean in 1933/1934.
In 1942, he organized a study trip to Prague, Vienna, Salzburg, Munich and Augsburg on the subject of "German Baroque and Rococo Art".
As director of the Kunsthalle, he tried to avoid confrontation with the Reichskulturkammer and to make exhibitions possible by means of suitable themes.
Under the motto "Zur Kunst der deutschen Stämme" [On the Art of German Tribes], he organized the exhibitions "Schlesische Künstler" [Silesian Artists] (1940), "Gäste aus der Reichshauptstadt" [Guests from the Reich Capital] (1942) and "Fränkische Künstler" [Franconian Artists] (1944), which were supported by public funds.
After the Second World War, the Kunsthistorisches Institut was briefly relocated to Schleswig in 1945, where Sedlmaier was represented by Lilli Martius [de] during the summer semester.