Glasgow-based contractor CCG (Scotland) completed the development as part of a £270m schools estate investment programme.
The new building has 13 classrooms, a gym, dining hall, music room and a library over its two stories.
Head teacher Lesley McCabe said: "We are absolutely delighted with the new building.
"It has everything we need to deliver the perfect curriculum to our children. It is more than we could ever have imagined and it will really motivate the children and bring out their creativity."
The new school has been built on a site next to the old school building which was opened 50 years ago.
Education & Communities Convener Councillor Jim Clocherty said: "It is interesting to think the new St Ninian’s has been completed half a century after its predecessor opened and in the centenary year of Catholic education in Scotland.
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"No detail has been overlooked in its construction and once again the designers, contractors and everyone involved in the project has delivered a school everyone in Inverclyde can be proud of."
hubWest Scotland helped deliver the project.
hubWest Scotland CEO Iain Marley said: "We are thrilled to have delivered St Ninian's school for our partner, Inverclyde Council.
"This investment has created an inspiring, flexible and sustainable learning environment that will benefit pupils and staff for decades to come.
"The school forms part of Inverclyde Council's commitment to transform the education estate and we are proud and privileged to have play a role supporting this hugely successful programme.
"This success would not have been possible without the leadership, clarity of direction and commitment to collaboration that has been consistently demonstrated by the Inverclyde team."
CCG Chairman and CEO, Alastair Wylie, added: "CCG have been operational in the Education sector for four years now but St Ninian's has been the largest contract undertaken so far.
"It is has everything that a modern primary school should have and we hope the pupils enjoy their new facilities. We thank Inverclyde Council and hub West Scotland for their continued support throughout the construction programme."
(CM)
