He assisted several set designers at the Wiener Volksoper and the Vienna State Opera, including Günther Schneider-Siemssen.
August Everding engaged him in 1973 as an assistant of Toni Businger [de] the Staatsoper Hamburg.
[1] From 1974, Marelli worked as a guest at the Theater Hagen, the Staatstheater Darmstadt, and at the Oper Frankfurt for stage directors Alfred Kirchner and Harry Kupfer.
From 1981, he also directed the operas for which he designed the set, beginning with Mozart's Die Zauberflöte at the Staatstheater Mainz.
[1] They worked together for the premiere of Aribert Reimann's Medea at the Vienna State Opera in February 2010, conducted by Michael Boder.