She studied in Milan with Vidal and made her debut at the Teatro Adriano in Rome as Micaëla in Bizet's Carmen on 31 October 1908.
In December 1910, she made her debut at La Scala as Carolina in Cimarosa's Il matrimonio segreto; the following year, she sang Octavian in the Italian premiere of Der Rosenkavalier there.
On the opening night of the 1912/13 season, she made her debut with the Met in New York when she sang Manon opposite Enrico Caruso.
She headed an organization called the Committee to Save the Metropolitan Opera House and, in actions that were widely reported in the press, she made appeals by flyer, letter, and in personal contacts with potential benefactors.
He said she "took command of the situation and applied to the fulfillment of the purpose in hand the same qualities of imagination and genius which have, in her own work made her one of the greatest artists of all time.
Bori sang scenes from Manon and La traviata, with contributions from Flagstad, Melchior, Rethberg, Pinza, Ponselle, Martinelli, Tibbett and Richard Crooks.
Bori continued to perform in recitals and record for some years after her Metropolitan retirement; she can be heard, for example, in "off-the-air" recordings of a Hollywood Bowl concert from 1937, singing "Si, mi chiamano Mimì" and "O soave fanciulla" with tenor Joseph Bentonelli, with the Los Angeles Philharmonic under Otto Klemperer.
Under her leadership the Guild collected musical instruments for military hospitals and performed other war activities as well as boosting opera throughout the country.