The vote of confidence was prompted by allegations of corruption surrounding the construction of a major arena project, Garden-Helsinki.
The votes against Orpo (Saml) were 101-90, Yle reports. In the vote on the government as a whole, the figures were the same.
Before the vote, parliament held a nine-hour debate on the issue.
Uncertainties surrounding the award of hundreds of millions in government funding for the large arena project led the opposition to demand the prime minister's resignation.
On Monday, Orpo announced that the project in its current form no longer has government support.
Parliament was summoned during the middle of the summer recess, which is rare in Finland.
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