After studying at Stuttgart's Music Academy, Hauptmann entered the Conservatory in Bern, Switzerland, where he continued his training as a pupil of bass Jakob Stämpfli. Upon receiving his diploma, he undertook master classes with several great artists of the previous generation, Elisabeth Schwarzkopf, Hans Hotter, and Dietrich Fischer-Dieskau most prominent among them. Hauptmann made his formal stage debut at the Stuttgart Staatsoper in 1981, remaining with that theater until 1989. At first assigned to small parts, he eventually graduated to the role of Masetto and thereafter was heard mostly as principal characters. From 1985 to 1987, Hauptmann was also engaged at Heidelberg, where he was heard as Osmin, Sarastro, Sparafucile, and Mozart's Figaro. Guest appearances took him to Paris, Frankfurt, and Reykjavik and he began singing at a number of important European festivals; Aix-en-Provence and Schwetzingen were among the first on a list that came to number in the dozens.
In 1991, Hauptmann appeared in a concert performance of Die Entführung aus dem Serail at London's Royal Festival Hall. That same year, he sang Sarastro at the Deutschen Oper Berlin; four years later, he appeared as Sarastro at Lyon. In 1988, he sang Mozart's Requiem with Bernstein and made an appearance at Salzburg as bass soloist in Mozart's Mass in C minor. By the new millennium, Hauptmann had also been heard in the major opera houses of Munich, Leipzig, Madrid, Lisbon, Amsterdam, Zürich, and Orléans.
In addition to two recordings of Sarastro and Philip Glass' Akhnaten, Hauptmann is heard as soloist on CDs devoted to Schumann's Das Paradies und die Peri, Enescu's Oedipe, and oratorios of Schütz, Haydn, Mozart, Beethoven, and Mendelssohn. Lieder recitals for Naxos and Bayer are devoted to songs of Schubert and Loewe.