In a famous incident about this time, Giardini, who was serving as assistant concertmaster (i.e., leader of the orchestra) during an opera, played a solo passage for violin which the composer Niccolò Jommelli had written.
Although the audience applauded loudly, Jommelli, who happened to be there, was not pleased and suddenly stood up and slapped the young man in the face.
For many years, he served as the orchestra leader and director of the Italian Opera in London and gave solo concerts under the auspices of J. C. Bach with whom he was a close friend.
His identity with the "Signor Giardini", who in 1774 sought with Dr Charles Burney to form a public music school associated with the Foundling Hospital, is uncertain.
His chamber music combines the so-called Style Galant with the mid-18th-century classicism of J.C. Bach, the Stamitzes and the Mannheim school.
Bramham was a seat of George Fox-Lane, later created Baron Bingley, whose wife Harriet was Giardini's most consistent patron.