Joan Sisiati Tahafa Viliamu (born 22 March 1966) is a Niuean politician and Cabinet minister.
Viliamu was born in Tuapa and educated at Matalave Primary School and Niue High School Intermediate.
She worked as a public servant and businesswoman before being elected to the Niue Assembly on the common roll at the 2011 election.
Following the election she was appointed to Cabinet as Minister of Health, the Community Sector, and Minister for the Niue Broadcasting Corporation.