Sanmartino was born in Naples. His first dated (1753) work is The Veiled Christ or Christ lying under the Shroud, commissioned initially from the Venetian sculptor Antonio Corradini who did not live to complete the work. Sammartino interpreted his sketches freely to create a masterful sculpture which can be seen in Sansevero Chapel (also called Capella Sansevero de' Sangri orPietatella) in Naples. Other contributors to this chapel were Francesco Celebrano and the Genoese sculptor Francesco Queirolo.

The statue of Veiled Christ is elaborately artificial (arti historian Wittkower labeled it as a hypertrophic effort) by reproducing in stone, the effect of a thin veil. In the same chapel, Corradini's antecedent statue of Chastity(also called Modesty) is present.