André George Louis Onslow was born at Clermont-Ferrand on 27 July 1784 to an English father, Edward Onslow, son of the first Earl of Onslow, and a French mother. In his own brief autobiography he wrote that music was only a secondary part of his education, but named Dussek and Johann Baptist Cramer among his piano teachers — the Dussek lessons probably taken in Hamburg in 1797–98, where the family was living in exile after his father’s involvement in counter-revolutionary activity in France; there is no evidence for the sometimes-repeated claims that he ever visited Vienna or met Beethoven. He was wealthy enough never to need critical or financial support, learned the cello, and played Mozart, Haydn and Beethoven quartets with local amateurs. He died on 3 October 1853.

He dated his musical life to hearing the overture to Méhul’s Stratonice in Paris in 1801: he wrote that the emotion penetrated him with feelings he had not known, that the veil hiding music’s beauties was torn, and that it became the source of his most intimate joy and the companion of his life. He wrote his first string quintets and quartets immediately, with no composition training at all, and published them at his own expense; Fétis observed that he at least had the leisure to overcome the gap. In 1808 he began studying composition with Anton Reicha in Paris. Chamber music was his main work, alongside four symphonies and four operas, and his position and means let him follow a path closer to his German Romantic contemporaries than to most French composers of the day — his following in Germany and England was correspondingly strong. Critics esteemed him in his lifetime, his reputation collapsed after his death, and it has been recovered only recently.

Sources:

• https://en.wikipedia.org/wiki/George_Onslow_(composer)
• https://www.wikidata.org/wiki/Q380935