In Hamburg Graupner got a job as harpsichordist at an opera house; for this theater he wrote five operas between 1707 and 1709. These were in an eclectic musical style, part German and part French (which was true of the language of each libretto, as well as the musical elements), and were extremely popular with the Hamburg audience.
In 1709 he took the job of vice-Kapellmeister with the Landgrave of Hesse-Darmstadt, rising to the top position in 1712. Graupner focused on operatic composition at the Darmstadt Hofkapelle, at one point supervising some 40 musicians. After the financial cutbacks of 1719, though, Graupner cut the size of his staff and gave up on opera, turning his attention to orchestral and instrumental music and cantatas. By 1723 Graupner had gotten himself named as Telemann's successor at the Thomaskirche in Leipzig, but when the Landgrave raised his pay and gave him other incentives to remain in Darmstadt, the Leipzig job fell to the second choice, J.S. Bach. Firmly entrenched in Darmstadt, Graupner took on many students, including Johann Friedrich Fasch, and wrote nearly as prolifically as Telemann: more than 100 "symphonies" (really three-movement sinfonias or multi-movement dance suites, all in major keys, and most dating between 1746 and 1753), half as many concertos (mainly for woodwinds, half in the three-movement Vivaldi pattern and the others in four movements), more than 1,400 church cantatas, and a sizeable number of chamber works and keyboard suites fusing French and Italian styles (he was apparently an exceptional harpsichordist). Graupner was also highly regarded for his accurate, elegant copies of the scores of other popular composers of the day, including those of the Mannheim school, and his more than 50 Christmas cantatas, in particular, reflect his familiarity with those more innovative composers. Blindness ended his career in 1754.