About 2300 people, young and old, marched from the Dental School in Great King St, along George St, around the lower Octagon and stopped on the upper Octagon lawn on Saturday.
As the first line of protesters reached the lawn, the last line of protesters, about 10 people deep, reached Hanover St.
Some stunned shoppers spoke of the size of the rally.
''Have you ever seen a bigger procession?'' a shopper asked.
Some protesters wore Guy Fawkes masks, several walked dogs and others pushed their children in strollers.
Molly George, of Dunedin, said she brought her son William Hardisty (2) on the rally because she was trying to raise an ''active citizen''.
''It's good for him to be a part of these things.''
Former children's television presenter Olly Ohlson, of Dunedin, said he attended the rally and held a sign with the words ''con job'' because of the ''stupid secrecy'' of the TPPA.
''Why the hell is John Key covering all this up?''
More than 100 signs on display included slogans such as ''TPPA big biz theft'', ''taking power from people'' and ''we can't agree on what we can't see''.
Musician Steve King performed and several people spoke in the Octagon.
They included Green Party co leader Metiria Turei, who praised the size of the crowd.
''You are enormous and beautiful ... ,'' Ms Turei said.
''We are here as part of a national day of action, part of an international movement that opposes the elimination of people's sovereignty, in favour of corporate power.''
The protest was one of more than 20 across New Zealand.
