Very little is known about his early years; he probably studied with his famous uncle Andrea Gabrieli, who was also a composer, and organist at St. Mark's. Like his uncle, Gabrieli lived in Germany for several years, and was employed at the court of Duke Albrecht V in Munich from around 1575 until the Duke's death in 1579. Soon after that Gabrieli returned to Italy, and in 1585 became the organist for the Scuola Grande di San Rocco, a religious confraternity; he would hold that post for the rest of his life. That same year (1585), Gabrieli became organist at St. Mark's and, on his uncle's death in 1586, assumed his position as its principal composer (Gabrieli also edited a number of his uncle's compositions for posthumous publication).
At that time, Venice was a very cosmopolitan city and something of a musical crossroads. Much of the city's musical activity centered around St. Mark's Cathedral, which had long attracted many great musicians. The Cathedral's unusual layout, with its two choir lofts facing each other (each with its own organ), led to the development of what has been called the Venetian style of composition -- a colorful and dramatic style often involving multiple choirs and instrumental ensembles; many of Gabrieli's motets and other religious choral works are written for two or four choirs, divided into a dozen or more separate parts. Gabrieli also became one of the first composers to write choral works including parts for instrumental ensembles; the motet In ecclesiis, as an example, calls for two choirs, soloists, organ, brass, and strings. Gabrieli wrote a number of secular vocal works (most or all of them before 1600), and a number of pieces for organ in a quasi-improvisational style.
Gabrieli composed many purely instrumental works in forms such as the canzoni and ricercari, which had become increasingly popular in the sixteenth century. Several of these were published with some of his choral music in the collection Sacrae symphoniae (1597). This publication was very popular all over Europe and attracted for Gabrieli a number of prominent pupils, the best known of which were Heinrich Schütz (who studied with him between 1609 and 1612) and Michael Praetorius. More of Gabrieli's instrumental pieces were published posthumously in Canzoni e sonate (1615). Some of these works were particularly innovative: the Sonata pian e forte was one of the first documented compositions to employ dynamic markings, and the Sonata per tre violini was one of the first to use a basso continuo, anticipating the later trio sonata. His instrumental works are now seen as the culmination of the development of instrumental music in the sixteenth century.
From around 1606, Gabrieli suffered from a kidney stone that reduced his activities, and eventually led to his death.