The new business will rebrand under the name N200.
The merger doubles the size of N200, which has offices in Netherlands, the UK and Germany.
Bart Van Bijnen, chief executive of N200, said: "By doubling in size, we will be able to deliver more innovation, more functionality and more support to our clients. We will continue to extend the scope and boundaries of the registration function beyond simply capturing data and creating badges."
Nick Caplan, chairman of SO Group, said: "This merger strengthens our ability to support our clients on a global scale."
SO Group employs more than 300 people and has an annual turnover of more than £50 million.
N200 works with more than 600 events a year in 28 countries. Its clients include Brintex, Clarion Events, Fresh Montgomery and i2i Events Group.
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