Born in Rome he was the eldest of the 7 childrenn of Nicolo Clementi (1720–1789), a noted silversmith His father soon realized his son’s musical talent, and by the time the boy was seven had arranged private musical instruction for him. By age nine he was sufficiently proficient to be offered a position as church organist at the Chiesa di St Lorenzo in Damaso.
In 1766, Sir Peter Beckford (1740–1811), a wealthy Englishman twice Lord Mayor of London, visited Rome. He was impressed by the young Clementi's musical talent, and negotiated with Nicolò to take Clementi to his estate in Dorset, England. Beckford agreed to provide quarterly payments to sponsor Muzio's musical education. In return, he was expected to provide musical entertainment at the manor. For the next seven years Clementi lived, performed, and studied there.
In 1770 Clementi made his first public performance as an organist. The audience was reported to be impressed with his playing, thus beginning one of the outstandingly successful concert pianist careers of the period.
In 1774, Clementi was freed from his obligations to Peter Beckford. During the winter of 1774–1775 he moved to London, making his first appearance as a harpsichordist in a benefit concert on April 3, 1775. There he made several public appearances as a solo harpsichordist and served as conductor (from the keyboard) at the King's Theatre, Haymarket, for at least part of this time. His popularity grew in 1779 and 1780, due largely to the run-away sales of his newly-published Opus 2 Sonatas. His fame rose quickly, and there was enthusiastic talk in musical circles that he was the greatest piano virtuoso of the day, possibly of all times.
Clementi started a European tour in 1781. In Vienna, he agreed to enter a musical duel with Mozart for the entertainment of Holy Roman Emperor Joseph II and his guests. On December 24, 1781, at the Vienese court, each performer was called upon to improvise and perform selections from his own compositions. The ability of both was so considerable that the Emperor declared a tie.
From 1782, and for the next twenty years, Clementi stayed in England playing the piano, conducting, and teaching. Two of his students attained a fair amount of fame for themselves:Johann Baptist Cramer; and John Field (who, in his turn, would become a major influence on Frédéric Chopin).
Clementi took over the publishing firm Longman and Broderip. He also had offices at 195 Tottenham Court Road from 1806. The publication line, 'Clementi & Co, & Clementi, Cheapside' appears on a lithograph, 'Music' by W Sharp after J Wood, circa 1830s.
Clementi also began manufacturing pianos, but in March, 1807, the warehouses occupied by Clementi's new firm were destroyed by a fire, resulting in a loss of about forty thousand pounds. But the man's courage was indomitable. That same year, he struck a deal with Ludwig van Beethoven, one of his greatest admirers, that gave him full publishing rights to all of Beethoven's music in England.
In 1810, Clementi bagan to devote all his time to composition and piano making. On January 24, 1813, Clementi together with a group of prominent professional musicians in England founded the "Philharmonic Society of London", which became the Royal Philharmonic Society in 1912. In 1813 Clementi was appointed a member of the Swedish Royal Academy of Music.
Meanwhile, his pianoforte business had flourished, affording him an increasingly elegant lifestyle. As an inventor and skilled mechanic, he made important improvements in the construction of the piano, some of which have become standard in instruments to this day.
At the end of 1816 Clementi made another trip to the continent to present his new works, particularly at the Concerts Spirituels in Paris. He returned to London in June 1818, after stopping off in Frankfurt. In 1821 he once again returned to Paris, conducting his symphonies in Munich and Leipzig. In London he was becoming widely acclaimed as a symphonist: in 1824 his symphonies were featured in five of the six programs at the 'Concerts of Ancient and Modern Music' at the King's Theatre.
In 1826 Clementi completed his very large collection of keyboard studies, Gradus ad Parnassum, and set off for Paris with the intention of publishing the third volume of the work simultaneously in Paris, London and Leipzig. After staying in Baden and most likely making another visit to Italy, he returned to London in the autumn of 1827.
On December 17, 1827, a large banquet was organised by Johann Baptist Cramer and Ignaz Moscheles in his honour. Moscheles, in his diary, says that on that occasion Clementi improvised at the piano on a theme by Handel. In 1828 he made his last public appearance at the opening concert of the Philharmonic Society; and in 1830 he retired from the Society.