Gari was born Samu Gyula in 1909 in Mediasch, Nagy-Küküllő County, Austria-Hungary (now Mediaş, Romania), the youngest of a family of ten children.
In 1938, he made his operatic debut at Rome's Teatro Reale dell’Opera, when he substituted for Tito Schipa as Almaviva in Gioachino Rossini's Barbiere di Siviglia (The Barber of Seville) under the baton of Tullio Serafin.
[2] Composer Virgil Thomson, then music critic of the New York Herald Tribune, wrote "the vocal treat of the evening was Giulio Gari, who sang with beauty of voice, easy command of the heroic style and no hesitancy about the high notes."
Noel Strauss of The New York Times wrote of his Rodolfo in La Boheme that it provided "the most distinguished vocalism of the evening, he showed sensitivity and marked refinement of style, climactic and exciting."
When he performed both Turiddu in Cavalleria Rusticana and Canio in Pagliacci, rarely ever attempted, the New York Times lauded him for singing both parts "with their different tessitura and their severe demands on an artist's vocal and histrionic endurance", and for delivering each "with remarkable control of his fine voice and an unusual depth of human feeling.
Once during the Metropolitan Opera's annual seven-week tour he was flown to Boston to sing his first Don Carlo in a performance hailed as "sterling."
He also astounded everyone when he made last-minute appearances as the Duke in Rigoletto, Don Jose in Carmen, and Dimitry in Boris Godunov, on three successive nights.
[7] He performed in Kodály's Psalmus Hungaricus at Carnegie Hall, and in the American premiere of Ildebrando Pizzetti's L’Assassinio nella Cattedrale at the Empire State Music Festival.