Steve Merridew, an environmental design associate at BDP, won the environmental leadership award for his work on Manchester Garden City. The initiative aims to increase temporary green space on brownfield sites and encourage sustainable eating.
Miliband gave his backing the project when he visited BDP's Manchester studio last year during his campaign to become Labour leader.
Merridew said: "Garden City is about bringing public and private sector organisations together to create biodiverse environments for the people and wildlife of Manchester city centre."
The leadership award recognises 18- to 39-year-olds who exemplify the best attributes of the city's young people.