Balfour Beatty Civil Engineering, BAM Nuttall, Osborne and Ipswich-based Jackson Frameworks have all won places on the framework.
The four-year programme will cover extensive civils and technology works to cut congestion on the bridge and strengthen an associated concrete structure.
Civils works at Dartford are planned to include new signalling gantries, demolition of existing toll booths and realignment of carriageways.
The contract also covers all associated kerbing, drainage, services diversions, lighting, fences and gates and traffic management.
Technology works include installing signs and signalling, vehicle height and width sensors, new traffic signals and road barrier systems, ramp metering and CCTV.
They will work for the Connect Plus consortium of Balfour Beatty, Skanska, Atkins and Egis.