The firms, whose work has included New York's Times Square, are tasked with transforming the 10,000-square-metre space at the centre of one of the largest urban renewal projects in Australia.

It is another step forward for the long-stalled project, which was previously known as Civic Place and has been on the drawing board for more than two decades.

Plans are in the early stages so there is little detail about how the 250-metre-long space will look, but design options are expected to be presented in August.

Landscape architect Anton James, from Sydney-based firm James Mather Delaney Design, said the space would become a symbol of the "new Parramatta".

The public space, he said, was unique in Sydney because of its size and it was "crucial" to the success of the bigger project.

"It's something you don't get very often. It's an opportunity to rebuild the heart of the city," Mr James said.  "It definitely needs to be somewhere people are drawn to, where they feel comfortable. It is the Town Hall steps, in a way."

The other firms selected were Copenhagen-based Gehl Architects and Australian firms Taylor Cullity Lethlean and Tonkin Zulaikha Greer.

They have worked together on projects including the Paddington Reservoir Gardens, the National Arboretum in Canberra and Victoria Square/Tarndanyangga in Adelaide.

Professor Callum Morton, the head of fine arts at Monash University and an artist, will develop a public art masterplan for the space.

Professor Morton said he wanted to commission high-quality work that would engage the public.

Art that had a practical function, such as Sydney's proposed milk crate-shaped pavilion, could be an element of the project as well.

"You can often make work that creates a lot of chatter but the work itself is quite weak or cheap so the chatter is cheap," Professor Morton said.

"What you want is something that is rich, that has many layers and can be engaged with in many ways. That kind of complexity stands the test of time."

How many works of art would be commissioned, the budget for their purchase, or where they will be located has not yet been determined, he said.

Parramatta's  Liberal lord mayor Scott Lloyd said the NSW Transport Minister Andrew Constance had this week given him assurance the proposed Parramatta light rail would pass close to the redevelopment.

"I think the public space is one of the most important aspects of the whole Parramatta Square. It is the make or break of that whole area," he said.

The major Parramatta Square developments all form a border around the space, which runs from Smith Street to St John's Anglican Cathedral.

Construction has started on one of the developments, the University of Western Sydney's new Parramatta City Campus.

No development applications have been presented for the other buildings but Parramatta Council has approved the demolition of its own offices and is relocating staff in a bid to hasten the process.

The Commonwealth Bank is considering moving into the square when its lease at Sydney Olympic Park expires in 2018-19 but says no decision has been made.

Design options for the public space are expected to be presented to the council for approval in August and its construction will be completed in stages. Under the best-case scenario, the overall Parramatta Square project would be finished by 2019.