[2] Lehtinen made his operatic debut in Helsinki in 1948[2] as Papageno in Mozart's Die Zauberflöte,[1] leading to his engagement at the Finnish Opera.

In 1958, he appeared in the title role in the world premiere of Casimir von Pászthory's Tilman Riemenschneider [de] at Theater Basel, alongside Montserrat Caballé.

[3] On 12 June 1958, Kullervo by Jean Sibelius received its first complete performance of the twentieth century, having been resurrected by the composer's son-in-law, Jussi Jalas.

[2] His roles there, and also at the Savonlinna Opera Festival, included Mozart's Leporello in Don Giovanni, Don Alfonso in Così fan tutte, Escamillo in Bizet's Carmen and Porgy in Gershwin's Porgy and Bess in 1964.

[2][5] Further roles included Wolfram in Wagner's Tannhäuser, John Sorel in Menotti's The Consul, the Man in Schönberg's Die glückliche Hand and Valentin in Gounod's Faust.