She took lessons in piano, phonetics, and diction before studying singing 1934-44 first with her mother, then with Salvator Issaurel, and finally with Pauline Donalda. In 1938 she placed first in her competitions in the Quebec Music Festival and won a silver medal. She sang often 1940-50 on Montreal radio stations CKAC and CKVL and on the CBC, gave recitals in the other provinces, and undertook several roles for the Opéra national du Québec and the Variétés lyriques. Her roles for the latter included Antonia in The Tales of Hoffmann in 1942. The same year, she created Josette in the premiere of Eugène Lapierre's comic opera Le Père des amours. In 1948 she won CBC radio's 'Opportunity Knocks' and made her debut at the Opera Guild as Gilda in Rigoletto. She sang this role 'with an infinite regard for truth,' according to Jean Vallerand of Montreal's Le Devoir, who also noted the mastery of technique evident in her remarkable vocal shading. With the violinist Noël Brunet and the pianist Gilles Breton she made one of the first three tours organized 1949-50 by the newly founded JMC (YMC).
In 1950 Létourneau went to Europe as soloist with the Disciples de Massenet and, on a grant from the Quebec government, stayed in France and Italy. In Paris she worked with Pierre Bernac; in Rome, with Luigi Ricci and Ré Koster. She gave radio recitals in France and took part in concerts conducted by Nadia Boulanger.
Back in Canada, Létourneau toured again 1952-3 for the JMC and frequently appeared on the CBC TV programs 'L'Heure du concert' and 'Concerts pour la jeunesse.' She completed her training at the CMM 1957-8 with Bernard Diamant, Dick Marzollo, and Otto-Werner Mueller. During the 1960-1 season, after a JM tour of 50 concerts in France as a member of a vocal quartet, she toured for the JMC in Maurice Blackburn'sSilent Measures.
Létourneau appeared as soloist with the MSO and the Quebec Symphony Orchestra and taught voice 1940-2 at Sherbrooke's Mont Notre-Dame, 1960-2 at the École Vincent-d'Indy, 1960-6 at the Institut Nazareth, 1962-3 at the Institut pédagogique de Montréal, and 1960-6 at the Grey Nuns' School in Hull. She also taught at Laval University 1966-84 and was a member of a vocal quartet there 1972-4.
See also Antonio Létourneau (her father).