The peaceful march was also organised to underline support for Catalonia's independence movement.
A separate demonstration by a direct action group turned violent on Saturday evening, as protesters targeted the police headquarters.
Spanish unionists plan to hold their own mass rally in the city on Sunday.
Nine separatist leaders were jailed on 14 October by Spain's Supreme Court for between nine and 13 years after being convicted of sedition.
The days that followed saw some of the worst violence in the history of the modern independence movement, which prides itself on its peaceful tactics.
What happened on Saturday?
Grassroots independence groups had urged independence supporters to fill the streets but said they were committed to peaceful protests, Reuters news agency reports.
A sea of protesters stretched from the city's waterfront to the landmark Sagrada Familia church.
"It is time to sit down and talk," one protester told Reuters. "I think it is time for the state to find a solution because it seems that this has no end and we are always at the same point. We have come here because we are fed up with so much repression that we have suffered from the state."
"We have always defended non-violence," said another. "What is happening in Barcelona is not a reflection of us, we separatists are not violent, we want our country, we want to be free."