With all precincts reporting, she got 60% of the vote.
Cowell informally declared her victory Tuesday night at a watch party at Birdie's restaurant in downtown Raleigh. She would be the city's 63rd mayor.
"While they have not called it, I'm comfortable calling it, that we won," Cowell said to her supporters.
Janet Cowell optimistic she'll be next mayor of Raleigh
The 56-year-old Democrat has lived in Raleigh since 1997. Now, after nearly a decade out of politics, she said what she saw from the political sidelines was part of the reason for jumping back in.
Cowell is a former member of the state Senate and Raleigh City Council.
She said she hopes to ease the tensions on the city council and bring energy back to downtown.
Finishing behind her were Paul Fitts (18%), Terrace Ruth (11%), Eugene Myrick (6%) and James L. Shaughnessy IV (4%).
Raleigh's Next Mayor: Meet candidate Janet Cowell