Led by the British group Republic, campaigners from Sweden, Denmark, Norway, the Netherlands, Belgium and Spain are due to come to London on April 29.
The group is planning to protst against the cost of raxpayers bankrolling European royal families.
Despite largely positive public reaction for the wedding, Republic campaign manager Graham Smith believes Britons are less excited about the day than the press coverage suggests.
"Most people in this country aren't that bothered about the royal family or the monarchy, they don't really care that much one way or the other," he said.
"When these big stories come up it then makes people think about it. It gives us opportunities to gain publicity and raise our profile."
An alternative street party will be held and merchandise such as cups bearing the pun "I am not a royal wedding mug" will be on sale, with the anti-celebrations culminating in a meeting of the European movement.
Republic, Britain's main republican campaign group, has seen its membership jump by around 50 percent to more than 14,000 supporters since William and Kate announced their engagement in November.
Campaigners also point to the fact that previous royal weddings have helped boost interest in a republic and increase hostility to royalty, which they regard as an anachronism in the 21st century.
The Swedish Republican Association, which is sending three representatives to London, said the wedding of Crown Princess Victoria and Daniel Westling in June last year eroded support for the Nordic country's royals.
"A royal event makes people reflect on the institution of monarchy, and in Sweden many arrived at the conclusion that this is an outdated and rather bizarre phenomenon," said the group's Helena Tolvhed.
Membership of the Swedish group rose from about 3,500 to 7,500 in 2010, she added.
After the Swedish wedding, anti-monarchist groups from seven countries formed the Alliance of European Republican Movements to share ideas and nurture organisations just starting out.
The alliance will hold a meeting the day after Kate and William's nuptials.
"Norway is just getting started and they will see a more established group like the one in the UK or the one in Sweden. It does really motivate people and inspire people," Mr Smith.