In London at the King's Theatre Naldi made his debut in April 1806, in Due nozze e un sol marito by , and he continued to sing there in every subsequent season up to 1819. Notably, he appeared in English premieres of Mozart's operas: in 1811 as Don Alfonso in Cosi fan tutte and Papageno in The Magic Flute, in 1812 as Figaro in The Marriage of Figaro alongside Angelica Catalani, and in 1817 as Leporello in Don Giovanni. He also played Figaro in the London premiere in 1818 of Rossini's The Barber of Seville, alongside Manuel García. He was in many other operas including Le cantatrici villane by Valentino Fioravanti and Il Fanatico per la musica by Simon Mayr. In the latter, he showed his skill in playing the cello.
