"We must not and we cannot allow this to continue," said Michel Vandenbosch, president of Belgian animal rights group GAIA. "An EU-wide ban is the way forward to end this unacceptable and indefensible cruelty."
He said up to 1,000 people joined the rally but police could not immediately confirm the figure.
Beatles legend Paul McCartney, who has been a strong critic of Canada's annual seal hunt, sent a special video supporting Tuesday's protest.
The EU is under pressure from animal rights groups and some lawmakers to take action over seal hunts, which they call cruel and inhumane. Activists have called for a total hunting ban that would affect Canada, Russia, Namibia, Greenland and EU members Finland and Sweden. Canada has the world's largest commercial seal hunt.
EU Environment Commissioner Stavros Dimas is expected to propose a ban on the sale of products from seals that have been inhumanely killed.