At the 1928 Summer Olympics in Amsterdam, he won a bronze medal in the 400 metres event. Four years later, he failed to reach the 400 metres final at the next Olympics, and finished in fourth place with the German 4 × 400 m relay team.
He won three national titles in the 400 m in 1927–1929 and finished second in 1925, 1931 and 1932. In 1928 he became the first German athlete to run 400 m within 48 seconds.
Büchner was a graphic designer and advertising consultant. After retiring from competitions, he worked at ASV Köln, first as athletics coach (1947–1950), then treasurer (1962–1969) and later as president (1969–1977). Until his death in 1978 he was a member of the Association of Former Track and Field Athletes of West Germany. Büchner's daughter Christa (born 1931) became a pentathlete.
