Porpora's first opera, Agrippina, was successfully performed at the Neapolitan court in 1708. His second, Berenice, was performed at Rome. In a long career, he followed these up by many further operas, supported as maestro di cappella in the households of aristocratic patrons, such as the commander of military forces at Naples, the prince of Hesse-Darmstadt, or of the Portuguese ambassador at Rome, for composing operas alone did not yet make a viable career. However, his enduring fame rests chiefly upon his unequalled power of teaching singing. At the Neapolitan Conservatorio di Sant'Onofrio and with the Poveri di Gesù Cristo he trained Farinelli, Caffarelli, Salimbeni, and other celebrated vocalists, during the period 1715-1721. In 1720 and 1721 he wrote two serenades to librettos by a gifted young poet, Metastasio, the beginning of a long, though interrupted, collaboration. In 1722 his operatic successes encouraged him to lay down his conservatory commitments.
After a rebuff from the court of Charles VI at Vienna in 1725, Porpora settled mostly in Venice, composing and teaching regularly in the schools of La Pietà and the Incurabili. In 1729 the anti-Handel clique invited him to London to set up an opera company as a rival to Handel's, without success, and in the 1733-1734 season, even the presence of his pupil, the great Farinelli, failed to save the dramatic company in Lincoln's Inn Fields (the "Opera of the Nobility") from bankruptcy.
An interval as Kapellmeister at the Dresden court of the Elector of Saxony from 1748 ended in strained relations with his rival in Venice and Rome, the hugely successful opera composer Johann Adolph Hasse and his wife, the prima donna Faustina, and resulted in Porpora's departure in 1752. From Dresden he went to Vienna, where he gave music lessons to the young Joseph Haydn, who lived with Porpora as accompanist and in the character of a valet, but allowed later that he had learned from the maestro "the true fundamentals of composition". Then Porpora returned in 1759 to Naples.
From this time Porpora's career was a series of misfortunes: his florid style was becoming old-fashioned, his last opera, Camilla, failed, his pension from Dresden stopped, and he became so poor that the expenses of his funeral were paid by a subscription concert. Yet at the moment of his death Farinelli and Caffarelli were living in splendid retirement on fortunes largely based on the excellence of the old maestro's teaching.
A good linguist, who was admired for the idiomatic fluency of his recitatives, and a man of considerable literary culture, Porpora was also celebrated for his conversational wit. Besides some four dozen operas, there are oratorios, solo cantatas with keyboard accompaniment, motets and vocal serenades. Among his larger works, his 1720 opera Orlando, one mass, his Venetian Vespers, and the serenata Arianna in Nasso (1733 according to HOASM) have been recorded .
He was well-renowned as vocal composer, yet his work Semiramide riconosciuta shows his great skill as orchestrator: its instrumentation is unusually ample, often in ten parts, with flutes, oboes, bassoons, French horns and trumpets that are listed and usually always very present. Porpora shows that not only does he know all the innovations in the technique of instrumentation, he also proposes color and impasti in continuous mutation. The work is filled with brief phrases, that pass from tutti to soli and vice-versa gently with much difference from the famous technique a terazze (which juxtaposes sections with fixed timbre and intensity). Vocal parts are extremely difficult, and if Mirteo indulges himself in moderate and amorous arias (maybe to showcase Farinelli's expressive ability), great virtuosity is focused on Ircano's aria (one is often stupefied with continuous jumps, even in an interval of twelfth in Talor che il veno freme (I, 14), an aria with vibrant semiquaver figurations in the strings section. Impressive is the virtuosity of Il ciel mi vuole oppresso (III,3), always accompanied by amazing and continuous replies from the brass). Semiramide, whose vocality is broken, filled with doubt, introspective, has a great pathetic-pastoral moment (in an unusual 12/8 measure of Il pastor se torna aprile (II,5), grand aria with transverse flutes obbligati), which in the ample chant of the queen achievs tumults of changeable, unexpected, intense harmony.
In his youth Porpora had much gaiety, spirit and a ready answer, but with ageing he had outbursts of bad mood that was excusable because of his extreme poverty. He was well-read in Latin and Italian literature, wrote poetry and spoke French, German and English.