The 49-year-old Peduto won Tuesday's election in Pennsylvania's second-largest city, where Democrats outnumber Republicans 2-1.
Peduto, who's finishing his 12th year on Pittsburgh City Council, won a three-way Democratic race in the May primary.
His Republican opponent, Josh Wander, sold his home in early September moved to Israel to work as a security consultant. Lester Ludwig, an independent, is also a candidate.
At what was supposed to have been the first mayoral debate of the fall campaign, Peduto was the only candidate to show up.
Peduto will succeed Luke Ravenstahl, a Democrat who is not seeking another term.