Orquesta Nacional de España
Weller's first engagements as a conductor were in 1966, deputising at short notice for Karl Böhm. His conducting debut at the Vienna State Opera was in 1969, leading "Die Entführung aus dem Serail". He later served as "Generalmusikdirektor" (GMD) of Duisburg, Germany, for the 1971–1972 season. From 1975 to 1978, he was principal conductor of the Niederösterreichischen Tonkünstlerorchester. From 1994 to 1997, he was Chief Conductor of the Basel Symphony Orchestra, the last conductor with that title before the orchestra joined with the Radio Symphony Orchestra Basel to form the Sinfonieorchester Basel, and in parallel, was GMD in Basel. He also served as principal guest conductor of the Spanish National Orchestra from 1987 until 2002. Weller served as Music Director of the National Orchestra of Belgium from 2007 to 2012, at which time he became Honorary Conductor of the orchestra. In 2010, he became the first honorary conductor of the Trondheim Symphony Orchestra. He also became Conductor Laureate of the Stuttgart Philharmonic Orchestra and Associate Director of the Valencia Orchestra.