The staffer, said to have been hand-picked by Green minister Åsa Romson, was found to have ordered a kind of hallucinogenic fungus from the Netherlands.
"You do stupid things under the influence of alcohol" said the man to police.
He was sentenced to a suspended sentence and community service.
The spokesperson for Åsa Romson says to news agency TT that they know about the staff member's history when he was hired.
Drug laws are very tough in Sweden, where narcotics are widely seen as socially unacceptable.