An able French merchant, he spent around fifteen years in Constantinople , holding the post of 'merchant of the Grand Seignor.' He expanded the range of his know-how in the Ottoman capital, learning methods for the dyeing, weaving and spinning of textiles. In 1755 he moved to Smyrna to find out about new industrial techniques and then decided to take the skills he had acquired back to France , where he set about modernizing the factory at Saint-Chamond, raising it to the level of a 'royal manufactory.' In 1766 he published a travel journal with curious details on the most innovative industrial methodologies. Published in 1740 with the title Observations sur le commerce et sur les arts d'une partie de l'Europe, de l'Asie, de l'Afrique, et même des Indes Orientales, the work has an informative rather than literary value.

The journey he began in 1740 lasted for eighteen years: Flachat entered Italy by sea from Ventimiglia, calling at Genoa, San Remo and Livorno; he then headed inland, visiting Pisa, Lucca, Pistoia and Florence; he continued to Civitavecchia, Ostia, Rome, Velletri, Terracina, Gaeta, Capua, Naples, Herculaneum, Pozzuoli, Baia, Bologna, Loreto, Ancona, Fano, Pesaro, Rimini, Ravenna, Ferrara, Venice, Padua, Vicenza, Verona, Mantua, Reggio Emilia, Correggio, Modena, Parma, Piacenza, Cremona, Pavia, Milan and Turin. From there he went on to Switzerland, France, Germany, Austria, Hungary and Turkey. He made a second visit to Italy, this time pushing further south, as far as Algeria .