The ceremony is to be at 10am local time (2pm Lisbon time) in the General Assembly hall, with representatives of the 193 member states in attendance, diplomatic sources confirmed to Lusa News Agency.
It has yet to be decided who will represent Portugal at the ceremony.
Before the swearing-in of Guterres, there is to be a separate ceremony in homage to his predecessor, Ban Ki-moon, the South Korean, who ends his second five-year term as secretary general at the end of December.
Guterres’s five-year term begins on 1 January. This is to be the only ceremony to mark it.