Born in Fossombrone, in the Marches, Diamantini was active in Venice by 1663. His early training is not well documented. Although Malvasia suggested that he was trained in Bologna, it is likely that he studied in the minor, Mannerist-oriented studios of Venice in the 1640s. He stayed in Venice until 1698, when old age and failing eyesight prompted retirement to his hometown. His success in Venice was sustained by his good relations with the nobility. Probably through the intercession of one of his patrons, he received a royal grant of knighthood in 1663. A succession of aristocrats supported his career, and the bulk of his work appears to have been decorative frescoes and canvases for these patrons. Just few of his painted works survive, between them, the altarpiece for the church of San Moisè, in Venice.