In 1914, he won first prize in an international singing competition in Parma. His operatic debut came on October 15, 1914 when he played Enzo in Amilcare Ponchielli's La Gioconda in Rovigo, following which he was in great demand.
Gigli made many important debuts in quick succession, and always in Mefistofele: Teatro Massimo di Palermo (March 31, 1915), Teatro San Carlo di Napoli (December 26, 1915), Teatro Costanzi di Roma (December 26, 1916), La Scala (November 19, 1918), and finally the Metropolitan (November 26, 1920). (Two other great Italian tenors on the roster of the Met during the 1920s were Gigli's rivals Giovanni Martinelli and Giacomo Lauri-Volpi.)
Some of the roles with which Gigli became particularly associated during this period included Edgardo in Donizetti's Lucia di Lammermoor, Rodolfo in Giacomo Puccini's La Bohème and the title role in Umberto Giordano's Andrea Chénier, both of which he would later record in full.
Gigli rose to true international prominence after the death of the mighty Italian tenor Enrico Caruso in 1921. Such was his popularity with audiences he was often called "Caruso Secondo", though he much preferred to be known as "Gigli Primo." In fact, the comparison was not valid as Caruso had a bigger, darker, more heroic voice than Gigli's.
Gigli left the Met in 1932, ostensibly after refusing to take a pay cut. Giulio Gatti-Casazza, the Met's then General Manager, was furious at his company's most popular male singer; he spread numerous lies to the press, for instance asserting that Gigli was the only singer not to accept the pay cut. There were in fact several others, Lily Pons and Rosa Ponselle among them. And it is well-documented that Gatti-Casazza gave himself a large pay increase in 1931, so that after the pay cut in '32 his salary remained the same as it had been originally. Furthermore, Gatti was careful to hide Gigli's counter offer to the press, in which the singer offered to sing five or six concerts gratis, which in dollars saved was worth more than Gatti's imposed pay cut.
After leaving the Met, Gigli returned again to Italy, and sang in houses there, elsewhere in Europe, and in South America. He was criticized for being a favorite singer of the Italian dictator Benito Mussolini, and toward the end of World War II was able to give few performances. However he immediately returned to the stage when the war ended in 1945, and the audience acclaim was greater and more clamorous than ever.
In the last few years of his life, Gigli gave concert performances more often than he appeared on stage. Before his retirement in 1955, Gigli undertook an exhausting world tour of Farewell Concerts. This impaired his health in the two years that remained to him, during which time he helped prepare his Memoirs (based primarily on an earlier Memoir, fleshed out by a series of interviews). Gigli died in Rome in 1957.
On the other hand, Gigli's relationships with women were all tainted by scandal. He lied in his memoirs, saying that he was married six months earlier than he really was. This was to conceal that his wife Costanza was pregnant before reaching the altar. Gigli had two children with Costanza, Enzo and Rina. (The latter was a well-known soprano in her own right.) Later, Gigli is well-known to have had a second family with Lucia Vigarani, producing three children. Gigli is rumored to have had at least three other children with as many different women. Like Caruso, Schipa, Björling, Tagliavini, and other of history's greatest tenors, Gigli's exact number of offspring will probably never be known.
Gigli's emotional directness, which he infused into every phrase he sang, made him a natural in the realm of popular song. Whereas Caruso sang every song as if it was his last, Gigli made each song or aria sound so effortless as to give the impression that he could sing 20 more with equal ease. And he sometimes did: Gigli's stamina was such that, after an opera, a piano would be wheeled onto the stage, and Gigli would sing an improvised concert of 10, 20, sometimes 30 encores. Virtually all of these post-opera concerts were fundraisers for which Gigli did not receive a penny. Gigli sang like this for 41 years without interruption. It is likely that neither Gigli's vocal longevity nor durability will ever be surpassed.
His remarkable singing can still be appreciated in the numerous recordings he made, both acoustical and electrical, primarily for RCA Victor (formerly known as the Victor Talking Machine Company). RCA even recorded Gigli's final performance in Carnegie Hall in 1955 (This recital forms the fifteenth and final volume of Naxos's Gigli Edition).