From 1974 onwards, Vivier made his living as a composer.  He lived on commissions alone.  He composed every day, and most of his works were written from 1977-1983, the period of his mature style.  This was his most productive period, and also the period when his largest works were written.  Vivier developed a compositional method in which he predetermined the parameters of his works mathematically.  This let him write the music quickly and turn out many works.  His style was simple with an emphasis on melody—most of his works were vocal and monodic.  They were also lyrical like late-Romanticism.  He was more in tune with this time than his own—he didn’t like modern music very much.  This gives Vivier’s music a characteristic uniformity that some people felt inhibited his originality.  Vivier would throw other elements into his music (on critic called them “Vivier intrigues”) to give a piece more interest.  In the last year of his life he experimented with a slower and more studied method of composition without much success, and switched back to his usual formula.

Vivier’s compositional method was both intuitive and reasoned.  The parameters of his music, like length and proportion, are very well organized mathematically.  At the same time, intuition and inspiration are extremely important to Vivier.  He needs to feel close to his musical material; to live it.  A melody is often the base for a whole work.  Vivier would compose the melody and sing it to himself all day until it developed itself and took on a form.  This could be the larger form of a piece, as well as the organization of the smaller parts.  Vivier's way of composing was in part a reaction against the contemporary music which reflected that composing was equivalent to inventing structures.  Vivier rejected this approach to creating works of art, thinking that it was crazy to forbid all inspiration from musical emotion.  In an interview, he said "Some expressions of emotion are too subtle to be manipulated or interpreted by structuring instruments like mathematical models."

Vivier wrote all his own texts, often in his invented language.  This language was enigmatic and used to express his inner self.  He would write the words after the melody lines were already composed, and then apply the sonority of the sound of the work to the melody and rhythm to achieve the effect he wanted.  Vivier was criticized over the years for his compositional style, but at the time of his death, his “sound” was already being imitated by young Quebecois composers.  This is remarkable, since Vivier had only just matured as a composer when he was killed.