Nelson woman Rose Renton has been found guilty of offensive behaviour after rubbing rat poison on local MP Nick Smith in 2017, RNZ reports.
It was an act of protest against a local 1080 poison drop.
Dr Smith was the Environment Minister at the time - and on the day of the altercation, a poison control operation was underway for the Brook-Waimarama Sanctuary.
"People are entitled to express their opinions; however, throwing and rubbing poison on another person has been rightly confirmed by the court as offensive behaviour," Dr Smith said.
"I do worry about the number of ugly incidents like this that have occurred over poison use as pest control operations have been stepped up to protect New Zealand's native wildlife.
"I would encourage new Minister Eugenie Sage to step up the Government's education and information campaigns so New Zealand can better understand the threat to our native wildlife from introduced pests and how essential poisons are to ensuring that birds like our kiwis survive."
Ms Renton became a prominent campaigner for medicinal cannabis reform after she fought for her son Alex to be treated with CBD oil.
Alex became the first New Zealander to be treated with CBD after sign-off from then-Associate Health Minister Peter Dunne.