Between 1741 and 1756, Gluck set more than a dozen Metastasian librettos. Residing in London during 1745 and 1746, he encountered the operas of Handel (and may even have met the great man) and showed his skill playing the glass harmonica. For the next six years he was a traveling musician, crisscrossing between Europe's musical capitals—Dresden, Vienna, Hamburg, Copenhagen, Prague, Munich, Naples—with an itinerant opera troupe. He settled in Vienna in 1752 and was active there for more than two decades, becoming musical director at a local theater, responsible both for Lenten concerts and for productions of French opera comique.

The course of Gluck's career changed in 1761, when the Tuscan poet Ranieri Calzabigi arrived in Vienna. Full of the new ideas of the day concerning dramatic aesthetics, Calzabigi was the most notable and effective opponent of Metastasian opera seria, and in him Gluck found the ideal collaborator. The classicizing spirit and sharp point of Calzabigi's librettos for Orfeo ed Euridice (1762) and Alceste (1767) proved tailor-made for Gluck's austere, yet genuinely passionate, music. Both are majestic operas that avoid the vocal display characteristic of opera seria; plots unfold in a straight line, and music and action are powerfully integrated. Just as Calzabigi's terse dramas were a welcome change from the effusions and platitudes that marked opera seria, Gluck's melodic simplicity and chaste scoring, along with his reliance on arioso and his fluid sense of form, were necessary correctives to the florid musical styles of many opera composers. Orfeo ed Euridice, which premiered in Vienna right under Metastasio's nose, was hugely successful.

Gluck took over the financial administration of Vienna's main theaters in 1769 and had little success, nearly losing his shirt (he quit the next year). Soon he found a new mission, the renewal of tragedie lyrique, the French equivalent of opera seria. In Paris between 1774 and 1779 he produced two new masterpieces, Iphigenie en Aulide and Iphigenie en Tauride, and new French versions of earlier hits—Orphee et Eurydice  and Alceste. He spent his final years in Vienna, in semiretirement and declining health, but greatly honored by the Hapsburg dynasty.

An avant-garde figure in his day, Gluck was outdated by the time of his death, overtaken by Mozart and the younger Italians, who were all writing comedies. Gluck's music was a dead end: It lacked the variety of scoring and texture, the play of style, and the long-range harmonic schemes that would allow opera to advance as a dramatic art. Gluck's works quickly disappeared from the repertoire, though the transformation of operatic conventions that he helped bring about—a greater naturalness of action and an increased emphasis on visual and other nonverbal elements to energize the plot—had a profound influence on the genre.

Also important was Gluck's use of musical pictorialism: for example, his gloomy portrayal of the underworld in Orfeo, or his deft rendering of Orestes' psychological situation in Iphigenie en Tauride—when Orestes sings "Le calme rentre dans mon coeur," the ostinato in the violas shows he's anything but calm. These are among the numerous cases in Gluck where the music is the drama and where the composer set an example much admired by Berlioz and Wagner. With the recent revival of interest in him, there is a new opportunity for Gluck's works to be better appreciated.