In 2002, the Netherlands became the first country in the world to legalise euthanasia
Prosecutors said in a statement that the man is suspected of “participation in a criminal organisation whose object is to commit and/or plan the crime of assisted suicide”.
It remains illegal for somebody who is not a physician to help somebody to take their own life.
Prosecutors did not identify the suspect but the organisation he leads, called the Final Will Cooperative, known by the Dutch acronym CLW, confirmed that its chairman, Jos van Wijk, had been detained.
In a reaction, the cooperative said it “regrets” that the Public Prosecution Service has decided to arrest its chairman.
“Since its inception in 2013, the CLW has consciously acted within the law.”
The organisation said that it “looks ahead to the further procedure with confidence”.
Debate has been going on for years in the Netherlands about the possibility of legalising assisted suicide as a way of giving people control over the final phase of their lives and allowing distribution of a substance that people wishing to end their lives can take.
While the cooperative says that a majority of the Dutch population supports legalisation, politicians remain deeply divided.
The group, which has says it has more than 26,500 members, is pushing for a law change.
It filed a civil case against the Dutch state in April, arguing that the government is “acting unlawfully by denying its citizens the right to die with dignity under their own control”.
The case is expected to go to court next year.
In another case, earlier this year, prosecutors also arrested a 28-year-old man from the southern city of Eindhoven on suspicion of providing a “suspicious substance” to at least six people who took their own lives.
Prosecutors allege that he sold the substance from November 2018 until June this year.
He has not yet been put on trial.