During the summers of 1955 and 1956 with the Marlboro Festival in Vermont Tessier performed cantatas by Rameau and Bach and the soprano part in Schoenberg's Quartet No. 2, and sang the lieder of Adolf Busch with Rudolf Serkin at the piano. She was a finalist in the Metropolitan Opera Auditions of the Air, and also, by unanimous consent of the jury, received the first-prize medal at the 1957 Geneva International Competition for Musical Performers. That summer she sang Elvira in 10 performances of Don Giovanni for the Montreal Festivals, and in 1958 she appeared as Nanetta in Falstaff for the Opera Guild of Montreal.
While under contract 1959-60 to the Detmold Landestheater in Germany, Tessier's roles included Violetta in La Traviata, Dorotha in Weinberger's Schwanda, and Karolka in Janáček's Jenufa. She sang in other German cities, especially Hanover, where she was acclaimed for her performance in La Traviata: 'Micheline Tessier captivated the audience...the evening's success was due to her convincing artistry' (Hannoversche Presse, 11 Feb 1960).
On her return to Montreal Tessier worked with Bernard Diamant, made her debut at the Canadian Opera Company (Micaela in Carmen, 1961), gave recitals 1962-3 for Community Concerts, and performed on CBC radio and TV. With the tenor Jean-Louis Pellerin (d Montreal 9 Feb 2003) and the bass Gaston Germain she formed the Trio Canadien Bel Canto, which toured 1963-5 for the Jeunesses musicales du Canada (Youth and Music Canada). Tessier sang leading roles in TV productions of Stravinsky's Pulcinella, Menotti's The Telephone, and Bernstein's Trouble in Tahiti.
Soloist with the Montreal Symphony Orchestra in 1958 and 1963, the Quebec Symphony Orchestra, the McGill Chamber Orchestra, and the National Arts Centre Orchestra, Tessier also sang in 1965 with the Bordeaux Symphony Orchestra. At the Théâtre lyrique de Nouvelle-France she appeared with great success as Musetta in La Bohème (1962), Tosca (1963), Cio-Cio-San in Madama Butterfly (1964), and Fiordiligi in Così fan tutte (1970). She sang Eudoxie alongside Richard Tucker in a 1964 Carnegie Hall concert performance of Halévy's La Juive. In December 1968 she went to the USSR, sang Tosca and Cio-Cio-San in the opera houses of Odessa, Tbilisi, and Yerevan, and gave a recital of French songs on Moscow TV.
By 1971 Tessier was concentrating primarily on teaching voice and stage techniques. She taught 1967-9 at the École normale and 1969-74 at Université du Québec à Montréal (UQAM), where she staged chamber operas by Schubert, Chabrier, Roussel, and Delibes. After teaching 1974-6 at the Lionel-Groulx Cegep, she was head 1976-81 of the music department of the Marguerite-Bourgeoys College. She was actively involved within the JMC in Montreal as general director 1981-5, and artistic director 1985-90. She was a member of the board of directors of the Canadian Music Council 1977-82 and its president 1982-3 and also president 1983-4 of the Canadian Conference of the Arts. In 1994, the CCA made Tessier an honorary lifetime member.
In 1960 she married Gilles Potvin.
Bach - Vivaldi - Handel. Arts Quebec Instr Ens: J. Morin fl, Verdon violin, Salvetti violin, Onofreyo viola, Carpenter violoncello, M. Lagacé organ and harpsichord. 1965. Pirouette JAS 19003
Soirée chez Bach: Le Petit Livre d'Anna Magdalena. Quatuor double of Montreal, B. Lagacé organ and harpsichord, Courville conductor. 1966. Madrigal MAS 404-U
'Atelier lyrique du Rhin,' ibid, vol 18, Mar 1977
'La Charmante Micheline,' Soviet Union Today Feb 1969
'Profil,' Aria, printemps 1982
Bergeron, Carole [sic]. 'Learning to communicate the joys of music,' Forte, Dec 1989