Starting in 1823, he served his apprenticeship under sculptor Stefano Ricci (1765-1837), from whom Nencini adopted Canova's classicism.
In 1832, he executed a statue of Saint Nicholas, now lost, noted for its reproduction of the historical clothes and accessories.
In 1837, he showed a plaster model of what was deemed "the most beautiful of his works" (Saltini, 1862, p. 35), a lounging Bacchante in the act of eating grapes; he exhibited it again at Brera in 1838 and donated it to the Academy in Milan, where it remains today.
In 1837, he created the effigy of Guido of Arezzo, inventor of the musical score, for the twenty-seventh niche of the outdoor Loggiato of the Uffizi; it was inaugurated ten years later on 24 June 1847.
In 1838, Nencini created the tomb of Giovita Garavaglia for the Florentine basilica of Santissima Annunziata.