It's the first world title for the pair, which took the silver medal at last year's Olympics and bronze at the last two world championships.
This is Canada's first victory in the pairs event at worlds since Jamie Sale and David Pelletier won gold in 2001.
Thursday's victory capped a perfect season for Duhamel, from Lively, Ont., and Radford, from Balmertown, Ont., who have won gold in every event they've entered in 2014-15, including the Grand Prix Final, Four Continents championships and Canadian championships.
In Shanghai, the Canadians posted the top score in both the short skate and Thursday's free program, finishing with a total of 221.53 points.
Chinese skaters gave the home crowd something to cheer for by taking spots two through four.
Sui Wenjing and Han Cong won the silver medal with a score of 214.12, leapfrogging Pang Qing and Tong Jian, who got the bronze with 212.77.
Peng Cheng and Zhang Hao finished fourth with 206.63.
Canada's Julianne Seguin and Charlie Bilodeau finished eighth (178.03) and Lubov Iliushechkina and Dylan Moscovitch were 13th (169.91).