New York-based landscape architect James Corner Field Operations is to design the 23ha south plaza to include a visitor centre and playground.
The site is between the main stadium, the aquatics centre and the giant red ArcelorMittal Orbit.
Piet Oudolf will handle plants and horticulture, ad the winning design features a tree-lined promenade connecting spaces cultural programmes, food stalls and other attractions. The area will have a London’s South Bank feel and welcome the majority of visitors to the Park.
The practice is renowned for its contemporary design across a variety of projects including the award winning and widely acclaimed High Line in New York City, a public park built on a rail line elevated above the streets of Manhattan’s West Side.
The second competition was for a smaller space or 'north hub' in the north park to include a playground and visitor centre won buy British landscape architect LUC and erect architecture.
LUC will lead landscape design for the playground, with slides, turf-roofed structures, earth mounds and areas of sand in the North Park.
It will allow children to climb trees, build dens and go on nature trails, all within close proximity to a visitor centre with café, seating terrace and indoor multipurpose space.
The community building is blended into the surrounding parkland, with access roads and paths defined by sweeping arcs of trees.
More than 100 teams from Europe, Asia and North America entered the competition and LUC will work with the Legacy Company to firm up ideas, to be delivered by spring 2013.
Other members of the team are Tall engineers, service engineers Max Fordham, artist Ashley McMormick, quantity surveyor Huntley Cartwright, Children’s Play Advisory Service and erect architecture.
Judge Tim Gill said "The highly naturalistic landscape design and understated, flexible building, are ambitious yet subtle, and should fit well in the wider park. The outdoor space has great potential to offer immersive, challenging, engaging play."
Andrew Altman, chief executive of the Olympic Park Legacy Company said: "The winner really captured the character of the Park as a compelling destination. These spaces will be among the first public areas added to the Queen Elizabeth Olympic Park."
"It is another example of how legacy plans for the Park are more advanced than any other previous host Olympic city."
Altman added: "James Corner Field Operations and erect architecture really captured the character of the Park as a compelling destination.
Minister for Olympic Legacy, Bob Neill MP, said: "London 2012 will leave a legacy of innovative design and boundary-pushing design."
Mayor of London, Boris Johnson, said:
"These two winners now have the chance to put their stamp very firmly on the Queen Elizabeth Olympic Park for generations to come."