Weimar was delegated to the Federal High Court of Justice in Karlsruhe (Germany) from 1964 to 1968 as a judge of the state of North-Rhine Westphalia after being appointed as a judge at the Regional Court of Cologne in 1961. The appointment as a judge at the Higher Regional Court in Düsseldorf followed in 1968, and from 1970 to 1972 he was delegated to the Federal Constitutional Court of Germany, the highest Court of Germany. From 1974 until his retirement in 1994 Robert Weimar worked as a professor and holder of a chair for civil law, mercantile law and commercial law at the University of Siegen's Department of Law (Germany).