The measure will technically take effect next month, but the sections allowing legal marijuana possession do not go into effect until next summer.
Democratic Gov. John Kitzhaber won a historic fourth term; Oregonians have not chosen a Republican for governor since 1982.
Measure 92 trailed by 1.2%, with fewer than 51% of voters in opposition.
The opposition campaign to Measure 92 has raised over $20 million in fundraising; supporters have raised just over $8 million.
Drug use policies will remain the employer's decision if Measure 91 is passed.