In 1862 he had been appointed physician to the diplomatic delegation sent to Persia to establish relations between the newly created Kingdom of Italy and the Persian government. There in Tabriz, Lessona met Daud Khan, who told him about the new Revelation. He met often with Gobineau, who had then become the French Ambassador to Persia and the two became lifelong friends. Most of Lessona's information on the Bábi Faith came from these two sources, especially the latter. He found it difficult to get any first-hand information about the Babis, but did recognize, in 1962, that the successor to the Báb was living in Baghdad.

Lessona organized two-part conference on the Bábi movement that was held in December of 1880. The following year he published the proceedings of the conference in a small monograph called I Bábi. It was the first Italian historical testimony on the Bábí - Bahá'í Faith. [Bahá'í Tributes; Bahá'í Teachings; BW12p900]