Martinelli's debut at the Metropolitan Opera took place on November 20, 1913, as Rodolfo in "La Bohème", where the young tenor's easy high C and pure, silvery tone attracted favorable attention; he was a Met mainstay for 32 seasons, with 926 performances of 36 roles, appearing most often as Radames in "Aida"; "Otello"; Manrico in "Il trovatore"; Don Alvaro in "La forza del destino"; Calaf in "Turandot" and Dick Johnson in "La fanciulla del West"; but also as Arnold in "Guglielmo Tell"; Eleazar in "La Juive"; Enzo in "La Gioconda"; Don Jose in "Carmen"; Vasco de Gama in "L'Africaine"; Canio in "I pagliacci"; Pollione in "Norma". He also sang in Boston, San Francisco and Chicago, often trying out new roles there, before singing them at the Met.