He invented the system of staff-notation still in use, and rendered various other services to the progress of musical art and science. He was educated by and became a member of the Benedictine Order in the monastery of St. Maur des Fosses, near Paris.

Early in his career Guido observed the confusion which prevailed in the teaching and performance of liturgical melodies generally, and especially in his immediate surroundings.

His endeavours to improve these conditions by innovations in the current methods of teaching are fully described in his writings; these made him unpopular with his brethren in the order and led to his removals to the monastery of Pomposa near Ferrara, Italy. Here the same lot seems to have befallen him. Intrigues and calumnies caused him to ask for admission to the monastery of Arezzo.

The exact date of his entrance into this community is uncertain, but it occurred during the incumbency of Theudald as Bishop of Arezzo (i.e., between 1033 and 1036), and while Grunwald was abbot of the monastery.

His fame soon reached the reigning pope, John XIX (1024-1033), who sent three different messengers urging Guido to come to Rome and exhibit his antiphonary containing the liturgical melodies transcribed from the sign-notation heretofore in use into his own staff-notation.

Pope John was overjoyed at the ease with which he was enabled to decipher and learn the melodies without the aid of a master, and invited Guido to take up his abode in Rome, to instruct the Roman clergy in the new system, and to introduce it into general practice in the Eternal City.

Unfortunately the Roman climate made it impossible for Guido to accept the invitation of the supreme pontiff. He soon fell ill of Roman fever and had to leave the city. He now returned to the monastery of Pomposa. The abbot (also called Guido) and monks, who had caused him so much chagrin by their opposition to his innovations, now received him with open arms, admitted their former mistake, and urged him to become a member of the community. His stay at Pomposa seems to have been only of short duration, for he soon returned to Arezzo.

Regarding the remaining days of the reformer, traditional reports vary. M. Faulty (Studi su Guido Monaco, 1882) holds that Guido ended his days at Arezzo, while others are of the opinion, based upon the chronicle and other evidences of a Camaldolese monastery near Avellano, that Guido died there as prior in the year 1050.

Guido himself has left to posterity in his "Epistola Michaeli monaco Pomposiano" (reprinted in Gerbert's Scriptures, ii) a naive but lively description of his, for the most part, eventful life, its trials and bitterness, and his final triumph over the opponents of his innovations.