He began his news career in 1976, writing for the ultra-leftist daily Lotta Continua, belonging to the eponymous political entity, becoming its deputy director. He then worked for the Genoan daily Il Lavoro, as well as for Radio Popolare, the communist newspaper Il Manifesto and the weekly newsmagazine L'Espresso.
He then worked on television broadcasts on Rai Tre, among which Profondo Nord and Milano, Italia. His reporting coincided with the infamous years of bribery scandals, known as Tangentopoli (Italian for Bribesville), and the ascent of the Lega Nord separatist political movement - Lerner successfully portrayed in his shows the deep changes the country was experiencing.
He later served as director deputy director of the national newspaper La Stampa and briefly as director of news broadcasts for TG1 and Rai Uno. He publicly resigned after a selection of pornographic footage was mistakenly aired on prime time during his news broadcast, TG1. Along with his resignation, he revealed that a politician from National Alliance, Mario Landolfi, who also was the president of the parliamentary commission of vigilance regarding the public TV broadcasting service, asked him to favour an acquaintance of his in the TG1.
In 2010 he was denied visa to Syria, even after his friend and journalist Alix Van Buren defended him: "He often defends the Muslim communities in Italy and their right to have mosques ... he is an independent Jew, who doesn't belong to any lobby ..., he signed a petition written by a group of European Jews which opposes some of the politics of Israeli prime minister Benjamin Netanyahu".
|| Deputy editor in chief of La Stampa
| Editor in chief of TG1
|New title|| Host of Otto e mezzo
|New title|| Host of L'Infedele