The proposals would see a 32-mile stretch of the highway widened from three to four lanes from Hayes, west London, to Theale, Berkshire.
This stretch of road, from junction three to 12, would also be subject to variable speed limits under the scheme.
Transport Secretary Chris Grayling, who granted planning permission for the scheme, said there is a “critical need to improve the existing national road network”.
READ MORE: All you need to know about smart motorways
In his letter of approval he said the plans will “increase capacity, improve traffic flow and reduce journey times, thereby supporting economic development”.
The proposals will see the stretch of road turned into a smart motorway, a government scheme aimed at increasing capacity without causing excessive disruption or becoming too costly.
Such schemes can fall into one of three categories – controlled motorways, dynamic hard shoulder running and all lane running.
Concerns have previously been raised with regards to all lane running schemes, with critics focusing on the distance between emergency rescue areas (ERAs).
With vehicles unable to stop in the hard shoulder when they come into difficulty, the ERAs provide motorists with a safe spot if they break down or are involved in an accident.
But the Commons Transport Committee launched a review of the distances between ERAs, which can be around 1.5 miles at most.
The MPs also called for an education programme to teach motorists about how to drive on smart motorways correctly.
READ MORE: Low Emission Zones: what you need to know
These fears have been echoed by the RAC, with the motorist’s champion having consistently raised concerns about the “lengthy spacing” between ERAs.
Work on the current M4 scheme is scheduled to begin in March 2017 and could take up to five years, with estimates suggesting it could cost between £586 million and £862m.
Louise Ellman, the chair of the Commons Transport Committee, has also voiced concerns about the project.
She said: “Breakdown operators say they will not go to cover broken down vehicles as they are concerned about safety. There is also concern that there will be too few emergency refuges.
“It will make traffic move more smoothly, but the question marks are over safety.”