The by-election on 22 March is the result of the death of Pa'u Sefo Taumata Pa'u last month.
Papalii, who is a lawyer by profession and a former assistant police commissioner was presented to the party by orators and chiefs from his village, Sapapalii.
Party leader and Prime Minister, Tuila'epa Sa'ilele Malielegaoi, was present with several cabinet ministers.
Papali'i will be running against another candidate from the party, the former Manu Samoa rugby team manager, Namulau'ulu Sami Leota.
