The prime minister Frank Bainimarama was among those who gathered to honour the late South African leader 100 years after his birth.
The declaration is aimed at redoubling global efforts towards peace and security, development and human rights.
Mr Bainimarama told delegates Nelson Mandela is an inspiration to all "of us who strive to respect and protect the human rights of all people".
"At home, abroad, in every encounter and exchange, we must engage with an open mind, we must strive for acceptance and understanding, and we must remain committed to peace and democratic ideals.
"That was Mandela's vision, and that is what is captured by the Mandela Declaration"
Frank Bainimarama said Nelson Mandela's legacy holds special meaning for Fijians who've suffered for decades under a political culture of division, hatred and disunity.