After having gathered almost 167,000 signatures, the supporters of the equal marriage could submit a bill to the Parliament to legalize marriage equality.
"Now it is time for Finland to join the group of countries which legalize marriage equality," Greens deputy Oras Tynkkynen said.
"Why would two fathers or two mothers be worse parents than a woman and a man?" he asked.
Within the government, the question divides. From a party to another, opinions diverge.
Currently, Finnish same-sex couples can be registered under a civil union. This initiative, if approved, would enable them to get the same rights as married straight couples notably as regards adoption.
The bill will be soon examined by a parliamentary committee for a vote.