Leclair was trained as a violinist, composer and dancer. He left his native Lyon and studied dance and the violin in Turin. In 1716, he married Marie-Rose Casthanie, a dancer, who died in 1728. Leclair returned to Paris in 1723, where he played at the Concert Spirituel, the main semi-public music series. In 1730 Leclair married for the second time. His new wife was the engraver Louise Roussel, who prepared all of his works from Opus 2 onward for printing. In 1733 he was named ordinaire de la musique by Louis XV but resigned in 1737 over control of the musique du Roy.

Leclair was then engaged by the Princess of Orange, a fine harpsichordist and former student of Handel. From 1738 until 1743 he worked in The Hague as a private maestro di cappella, returning to Paris in 1743. His only opera, Scylla et Glaucus, was first performed in 1746 and has been revived in modern times. From 1740 until his death, he served the Duke of Gramont.

Leclair was known during his lifetime as a virtuoso violinist as well as a composer. His numerous suites, sonatas, and concertos have all survived along with his opera, while some vocal works, ballets, and other stage music is lost.

In 1758, after the break-up of his second marriage, Leclair purchased a small house in a dangerous Parisian neighborhood, where he was found stabbed to death in 1764. Although the murder remains a mystery, speculation has focused around his ex-wife, who may have killed him for the money, but many have thought that his nephew, Guillaume-François Vial, is the most likely suspect.

His sonata in e minor for two violins is in three movements, mixing the practice of the baroque suite (a grouping of various dances) with the sonata (a group of various contrasting movements). The movements are; Allegro ma poco, Gavotte (andante grazioso) and Presto.