The article focuses on the figure of Giuseppe Moriani (doc. in Florence between 1706 and 1756), to whom we propose attributing the 'Martyrdom of Saint Andrew' in the church of the Conservatorio delle Mantellate in Florence, a painting traditionally assigned to his teacher Giovanni Camillo Sagrestani. The news that in 1715 Giuseppe Moriani painted a 'Martyrdom of Saint Andrew' for the Compagnia di Sant'Andrea dei Purgatori in Florence – published en passant by Anna Padoa Rizzo in an article on Cosimo and Bernardo Rosselli in 1991 – has never before now entered into any discussion on the painter. Nor, as a consequence, has there been any attempt to trace the painting. In this context, and from an analytical re-reading of the documents, various pieces of evidence have emerged that now make it possible to identify the work as that in the church of the Mantellate and therefore to establish an important chronology for Moriani's career as an independent artist. Through an analysis of the painter's critical fortune and sustained by the objectivity of the documentary information, a framework of stylistic and chronological references has been reconstructed that has been crucial in placing the work in question within Moriani's production. This new information has contributed to a better understanding of his artistic personality, one that has been rather neglected by scholars – who have usually dealt with it in a fragmentary way – and in any case always considered subordinate to that of his teacher and other painters of his circle like Matteo Bonechi and Ranieri del Pace.