The award, run by Keep Britain Tidy, pitted Victoria Park against 1,424 parks and green spaces in the annual poll and more than 7,000 votes were cast.
The park, which draws more than 275,000 visitors a year, reopened this year following a £12m redevelopment of the 86ha historic park, which was the biggest investment in the space since its creation in the 1840s.
New seasonal bedding contrasted aquatic plants and wildflower meadows around the perimeter. An old English herbaceous garden built in the 1800s was revitalised by Sarah Price, co-designer of the nearby Olympic Park and a pagoda was reintroduced.
Green Flag Award scheme manager Paul Todd said: "With more than 7000 votes for the People’s Choice Award, it is fantastic to see how much people value their green spaces, recognising the richness they bring to their lives.
"There is a fantastic range of winning sites from university campuses to cemeteries, proving that it’s not just traditional parks which provide places for people to relax and enjoy time out from the frantic pace of modern life."