Marie-Nicole Lemieux was born in 1975 in Dolbeau-Mistassini, Quebec. In 1994, Lemieux entered the Chicoutimi Conservatoire de musique and began studying voice with Rosaire Simard. After graduating with a degree in voice in 1998, Lemieux continued with graduate studies at the Conservatoire de musique du Québec à Montréal with noted teacher Marie Daveluy. Lemieux graduated with a Masters in voice in 2000 and found almost immediate success. In the span of three weeks, Lemieux won first prize at both the Jeunesse Musicale du Canada's Joseph Rouleau Competition in Montreal and the Queen Elisabeth International Music Competition for opera in Brussels in 2000. Lemieux also took second prize in the separate competition for Lieder at the Queen Elisabeth International competition. Lemieux's success was immediately followed with invitations to perform and/or audition with many of the world's finest orchestras and opera companies.
Lemieux has done concert and recital work with the Los Angeles Philharmonic, Montreal Symphony Orchestra, Orchestre National de France, Orchestre national du Capitole de Toulouse, Orchestre symphonique de la Monnaie, Orchestre Philharmonique de Radio France, The Academy of Ancient Music, the Rotterdam Philharmonic Orchestra, Les Musiciens du Louvre, the London Philharmonic Orchestra, the Deutsches Symphonie-Orchester Berlin, Ensemble Matheus, Les Violons du Roy, Ensemble orchestral de Paris, Modo Antiquo, the Singapore Symphony Orchestra, St. Petersburg Philharmonic Orchestra, Orchestre symphonique de Montréal, The National Arts Centre Orchestra in Ottawa, the Tafelmusik Baroque Orchestra, the Québec City Symphony, the Toronto Symphony Orchestra and the Edmonton Symphony Orchestra among others.
She has sung with many of the world's best conductors including: Richard Bradshaw, Franz-Paul Decker, Charles Dutoit, Paul Goodwin, Bernard Labadie, Sir Neville Marriner, Kurt Masur, Marc Minkowski, Kent Nagano, John Nelson, Gianandrea Noseda, Peter Oundjian, Michel Plasson, Federico Maria Sardelli, Michael Schonwandt, Marc Soustrot, Yoav Talmi, Ilan Volkov and Pinchas Zukerman among others.
In 2001, she won the Canada Council Virginia Parker Prize.
In 2002, Lemieux made her professional operatic debut in the role of Cornelia in Handel's Giulio Cesare with the Canadian Opera Company. An auspicious debut as the other cast members in that production included such opera greats as Daniel Taylor, Ewa Podleś, Isabel Bayrakdarian and Brian Asawa.