Although from an established family he is largely self-educated. He left school at 14, shortly after the suicide of his brother, the poet Sylvain Garneau. Michel Garneau was a radio announcer at 15. Garneau was well known in the 1950s and 1960s as host of various programs on Radio-Canada.
He wrote mainly poetry until his imprisonment during the October Crisis of 1970, an event that was crucial to his political awakening (a major collection, Les Petits Chevals amoureux, was published in 1977). In 1978, he is awarded the Governor General's Award. However, he refused it for political reasons. In 1988, his Poésies complètes is published. It includes 10 books of poems written between 1955 and 1987.
Garneau teached at the National Theatre School of Canada for over 20 years. In 1986, he becomes the school's francophone artistic director. Garneau is the author of some 50 plays to date, most of them produced and published, including important translations/adaptations of Shakespeare, Garcia Lorca and other major authors. Among his best known are Quatre à quatre (1973), staged frequently in Montreal, Toronto, France, Belgium, Italy, Spain, Germany and the US. A poetic exploration of the troubled lives of four generations of Quebec women, it is the first Canadian play included in the regular repertory of a theatrical company in France. Émilie ne sera plus jamais cueillie par l'anémone (1981), translated into English, German and Spanish, is a sensitive, imaginative portrayal of the American poet Emily Dickinson. Mademoiselle Rouge, first performed in Geneva in 1989 is a fanciful depiction of Little Red Riding Hood, now adult, reflecting on the central event of her troubled childhood, while Héliotropes presents another voyage of self-discovery, set in a ragtime bar.
A common characteristic of Garneau's plays is their use of popular Québécois speech, structured in flexible blank verse. Many are written to order, for institutions (the National Theatre School, Conservatoire d'Art Dramatique de Montréal (see Conservatoire de musique et d'art dramatique du Québec), Théâtre de l'Université de Montréal, etc.) or for major theatres (Théâtre d'Aujourd'hui and Théâtre du Rideau Vert).
Garneau also composes music and sings and performs professionally in a variety of venues. He has played important stage roles, particularly in plays by Michel Tremblay and Jovette Marchessault. Frequently labelled a "Jack-of-all-arts,", he is certainly master of most, and he tried his hand in translation in two works by Leonard Cohen: Étrange musique étrangère (Stranger Music) (2000); and Le livre du constant désir (Book of Longing) (2007). Garneau's Poèmes du traducteur and Les chevaux approximatifs were published in 2010. Michel Garneau received a Governor General's Award in 1989 for French language drama and that same he was awarded the prix Victor-Morin.