In the period between 1955 and 1962 Weiz was the first deputy manager at VEB Carl Zeiss in Jena. In July 1958 he became a member of the central committee of the SED. In July 1962 he was appointed minister of research and technology which he held until December 1966. In May 1963 he was made a member of the Research Council and served in the post until October 1966. From 1963 to March 1990 he served as a deputy at the People's Chamber. In 1967 he was named as the deputy chairman of the Council of Ministers or deputy prime minister. In 1974 Weiz was appointed minister of science and technology. In November–December 1989 he resigned from all of his posts, including his membership from the central committee of the SED.