Vivier’s style was unique, original, and personal; even autobiographical.  He was influenced by important works in our musical history, and by oriental music.  Although he was a student of Stockhausen, Vivier ignored the avant-garde principles of that time, which were against the expression of indiviuality in music.  Vivier's music is an interweaving of his personal and professional life.  His music was a means of communication that he constantly strove to perfect.  The themes in his music-- love, death, the lonely child (Vivier himself) searching for his spirituality, immortality, and afterlife-- were inspired directly and indirectly by Vivier's personal life.  They come from Vivier's unknown family origins, which haunted him all his life, his spiritual search, his life as a composer, and his homosexuality, all which contributed to lifelong feelings of loneliness and deep need for friendship.  Further personal influences were his great love for life, and preoccupation with death.  The same themes appear over and over in all of Vivier's music, and the texts to his music. Most of his music was based on dreams, and the dream-like texts (written by Vivier himself) to many of his vocal works are often surreal.

Vivier's spiritual search led him to the Eastern religions and to the island of Bali in 1976.  He later said in an interview that "all the rest of my music afterwards was more or less a tribute to Bali."  Vivier spent his life struggling to answer his spiritual concerns through music, and at the time of his death, he was still trying to resolve his ideas by writing Crois-tu en l’immortalite de l’ame.  Vivier has written:  "I think that the most important point about my music is its spiritual content.  God is the centre of my music."  Music was a way for Vivier to confront, as he wrote, "the total mystery which is the universe," and to find "the soul of humanity."  In a conversation, he once said that "Composing music should be like putting a Volkswagen on Mars."  In other words, music should juxtapose the world of our experience with the otherworldly.

Vivier's mature style (after his visit to Bali) is characterized by two things above all:  melody and colour.  It has been written about his music that "Melody is his starting point, and orchestral colour is his ultimate goal."  Most of his music is vocal, and often uses words from Vivier's invented language.   The music is usually monodic (a single line of melody), with little or no contrapuntal activity.  The melodies he uses are striking.  They are harmonized by a complex overtone series and set in varying textures.  The textures he produces are very simple and clear.  The harmonies and instrumentation that Vivier uses produce original and distinctive colours.  The music is panchromatic (using all keys), and the points of departure and arrival in the music are usually homorhythmic, and set in time to a complex arithmetical grid.  Most of Vivier's music is slow-paced, and his works are fairly long.   The music produced is very direct and expressive, and simple in melody, harmony, texture, and rhythm-- everything except the use of sonority.  Vivier often starts with the bare melody, and transforms it throughout the piece by adding more and more complex colours to it.  His work Lonely Child is a piece of music which is characteristic of Vivier's mature style.

The critic Harry Halbreich wrote about Vivier that “His music truly resembles that of no other composer, and finds its place quite outside all the current trends.  Its expression is direct and striking, but only the unfeeling, unable to classify this "ousider" genius, were disoriented by his music.  Claude Vivier had found what so many others sought and still seek:  the secret of a truly new simplicity.”