Born in Como, Vaghi studied singing in Milan before making his debut in Jules Massenet's Manon at the Teatro di San Carlo in Naples in 1925.
He sang a broad repertoire at that house, including appearances in the world premieres Ildebrando Pizzetti's Lo straniero (1930, King Hanóch), Ermanno Wolf-Ferrari's La vedova scaltra (1931, Innkeeper), Licinio Refice's Cecilia (1934, Bishop Urbano), and Franco Alfano's Cyrano de Bergerac (1936, Carbon).
In 1945 he signed a contract with the Metropolitan Opera, making his debut at the house on 18 February 1946 as Colline in La bohème with Dorothy Kirsten as Mimì, Jan Peerce as Rodolfo, Frances Greer as Musetta, John Brownlee as Marcello, and Cesare Sodero conducting.
He remained committed to that house for the next two and a half years, portraying Alvise in La Gioconda, Don Basilio in The Barber of Seville, Ferrando in Il trovatore, Nilakantha in Lakmé, Raimondo in Lucia di Lammermoor, Ramfis in Aida, Samuel in Un ballo in maschera, and Sparafucile in Rigoletto.
[2] Some of the other roles Vaghi created on stage were Alfonso in Lucrezia Borgia, Baldassarre in La favorite, Banquo in Macbeth, Basilio in Nerone, Blind man of Kinnèreth in Dèbora e Jaéle, Cacio in Il Guarany, Count Rodolfo in La sonnambula, Count Walter in Luisa Miller, Don Bartolo in The Barber of Seville, Don Fernando in Fidelio, Dosifey in Khovanshchina, the Gentleman in Fra Gherardo, the Grand Inquisitor in L'Africaine, Heinrich der Vogler in Lohengrin, Il Cieco in Iris, Jacopo Fiesco in Simon Boccanegra, Lotario in Mignon, Herrmann in Tannhäuser, King Marke in Tristan und Isolde, Le Comte des Grieux in Manon, Marco Orsèolo in Orsèolo, Margherita's father in Margherita da Cortona, Mathieu in Andrea Chénier, Mefistofele in Faust, The Miller in Il re, Milone in Giuseppe Mulè's Dafni, Padre Guardiano in La forza del destino, Pagano/Hermit in I Lombardi alla prima crociata, Philipp II in Don Carlos, Simone in Gianni Schicchi, Veit Pogner in Die Meistersinger von Nürnberg, and Walter Furst in William Tell, and the title role in Boris Godunov.