Niningi graduated from the University of Papua New Guinea with a Bachelor of Laws.

He was declared the winner of the seat on 14 August 1998 following a recount which was ordered by the Court of Disputed Returns.

He was appointed as Minister for Higher Education, Research, Science and Technology in the O'Neill-Abel Cabinet.

He was then appointed as Minister for Inter-Government Relations on 7 June 2019 as part of the First Marape Cabinet.

[1] Niningi was appointed as a Companion of the Order of St Michael and St George in the 2025 New Year Honours for his political service and for his service to the legal profession in Papua New Guinea.