Costain will start construction of the £32.3m bridge, which joins Walton and Shepperton along the A244 in Surrey, early this year after re-egineering the structure to cut costs by one-fifth.
The bridge project has suffered several delays, the most recent setback coming in October when ministers said that plans to replace the current temporary structure were too costly.
This prompted a cost-saving exercise that sliced around £6m from the estimated project cost by redesigning the foundations and transferring extra risk to Costain.
Carbon steel will be used instead of weathering steel, while further savings will be made by reusing excavated material.
Now the Department of Transport has now agreed to spend £23.8m with the rest of the cash coming from Surrey County Council.
Approving the scheme, local transport minister Norman Baker said: “The new bridge will bring long-term benefits for all those travelling in the area.
“Without this investment motorists would have faced huge disruption and delays as the temporary bridge reached the end of its life.”
Surrey County Council officers had warned that if building work did not start by March, planning permissions would expire, with a 12-month delay costing more than £1.3m due to inflation.
The council has be waiting for 57 years to replace two temporary bridges erected to replaced the original bridge damaged during the Second World War.