The June 24 race will be the 12th of 16 rounds in season nine. The championship starts in Mexico City on Jan. 14 and ends in London with a July 29-30 double-header.
The Indian city of Hyderabad, Cape Town in South Africa and Brazil's Sao Paulo are also debuting next season.
Miami, Long Beach and New York have previously hosted Formula E in the United States.
"There is a big, passionate fanbase for professional sports in the city, together with strong ecological credentials which makes Portland a perfect host," said Formula E co-founder Alberto Longo.
"The USA remains an important market for Formula E. We are delighted to maintain that critical presence and engage a new audience in the Pacific Northwest region in all-electric motorsport."
The city-based championship is entering a new Gen3 era in 2023 with faster, more efficient and lighter cars.
Maserati and McLaren, the latter taking over from Mercedes, have joined the championship.