Security personnel at the scene quickly wrestled down the perpetrator wearing clothing adorned with the logo of anti-immigrant group Soldiers of Odin.
Soini, former leader of the Finns Party who split to set up his own Blue Reform faction in 2017, told onlookers that his security detail apprehended the man attempting to strike him.
The incident did not deter Soini from continuing his meet-and-greet activities at the farmers' market in Vantaa’s Korso district.
"Today I faced an unfortunate incident, that nobody should want or hope for," wrote Soini on his blog. "The threatening situation was calmed quickly. I've told police what I saw and experienced. The matter is now being dealt with and investigated by the authorities. They know how to handle this. I thank the security men for their good work."
Attacks on politicians are rare in Finland. In 2012, a man pulled a knife on then-Prime Minister Jyrki Katainen at a municipal election rally in Turku. Three years later in Tampere a man doused Alexander Stubb, who was Finance Minister at the the time, in coke.