He received the honour in front of more than 140 guests at a special meeting of the City Council.
Mr Mann was nominated for the freedom in recognition of the example of achievement he has set to the city’s young people, and his personal contribution to the economic well-being of the city and people of Sunderland.
The Nissan plant now employs more than 7,000 people and, since first starting work there in 1985, Mr Mann has helped oversee many of its production and manufacturing milestones.
He said: ‘There is a spirit and enthusiasm that makes Sunderland a very special place. This approach to life was one of the key reasons why Nissan first decided to locate in North East England.
‘I am therefore honoured to be granted the Freedom of the City of Sunderland today and accept it with a huge amount of pride.
‘I would like to pay tribute to all my colleagues, the City Council and our many UK partners for the support they have given Nissan over the past three decades. They have all played a role in creating a new international automotive centre, here in North East England.’
A unique contribution
Mr Mann was awarded a CBE in the Queen’s 2012 New Year’s Honours List for his Services to Business in North East England.
Among the guests were the Lord-Lieutenant of Tyne and Wear, Nigel Sherlock, OBE. He is the Queen’s representative in Tyne and Wear.
Mr Sherlock said: ‘I am delighted the Freedom of the City of Sunderland has been bestowed upon Trevor, who has made a unique contribution not just to Sunderland, but to the whole of Tyne and Wear and the wider North East region, by promoting and leading the success of the Nissan team.’