The equal four-way alliance will deliver a rail route linking Oxford, Milton Keynes and Bedford, and Milton Keynes with London Marylebone via Aylesbury.
This will include a new station at Winslow, two new platforms at Bletchley, 18 new overbridges, 22 new footbridges or subways and changes to 97 railway crossings.
The firms in the alliance team are already working collaboratively to deliver the Stafford Area Improvements Programme.
Andy Milne, senior programme manager and alliance manager, said: “Never before on a project of this size has an alliance been convened this early.
“By scoping all aspects of the project now we will see potential problems early and be able to mitigate them. The earlier we do this work the greater value for taxpayers’ money we can deliver.”
The work will involve upgrading and reconstructing underused and mothballed sections of the railway linking the Great Western, Chiltern, West Coast and Midland main lines north of London and providing a strategic east-west route connecting key centres.
The news comes six weeks after the first passenger trains began running on from Oxford Parkway to London Marylebone via Bicester – the first new rail link between a major city and the capital in more than a century.
Once outline design work is complete, the EWR2 alliance will consult with the Department for Transport to agree a final design, construction timetable and costs.
It aims to submit an application for a Transport & Works Act order in autumn 2016.
Graeme Castle, rail sector leader for Laing O’Rourke, speaking on behalf of all the EWR2 partners, said: “We are all proud to be involved in this nationally significant project and aim to build on the success of the Staffordshire Alliance.”
The long-term aspiration of East-West Rail is to link Oxford in the west to Ipswich in the east, via Milton Keynes, Bedford and Cambridge – a journey that would currently require train passengers to travel via London.