The passive safety system (also called restraint system) includes up to nine airbags: two-stage adaptive airbags for the driver and front passenger, a kneebag for the driver, sidebags for driver and front passenger (combined thorax/pelvis bags), sidebags in the rear row of seats as an option, windowbags across both rows of seats from the A to the C-pillar, in addition to 3-point seat belts on all five seats with pyrotechnic reel tensioners and permanent belt force limiters as well as electrically reversible belt tensioners in the front, reel tensioners and single-stage force limiters for the outer seats in the rear.

Other safety equipments include ISOFIX child seat anchorage, belt height adjustment for driver and front passenger, belt status display for rear-seat passengers in the instrument cluster, an optional automatic child seat recognition (ACSR) with deactivation of the front passenger airbag if a special Mercedes-Benz child seat is used.

In a rear-end collision, a passive head restraint system can reduce the forces exerted on occupants.

Other passive measures contribute to pedestrian safety and include, for example, the installation of an Active Bonnet as standard.

Standard equipment forming part of the safety concept of the new M-Class includes the anticipatory safety system PRE-SAFE, which combines active and passive safety synergies to reduce the loads exerted on the vehicle occupants in the event of an accident.

Depending on the potential accident situation detected, the following reversible measures can be initiated for preventive occupant protection:

- Driver and front passenger seat belts are tensioned,
- Windows are closed,
- Sliding sunroof is closed,
- Front passenger seat is adjusted (when fitted with memory package).

The safety system can detect an impending rollover in the event of crash and if necessary deploy the head, side and window airbags, as well as the seat belt tensioners.

The standard active safety equipment package includes the drowsiness detection system ATTENTION ASSIST (warns the driver of drowsiness) the tyre pressure loss warning system, as well as adaptive brake lights (warns vehicles behind in an emergency braking situation with flashing brake lights) and Brake Assist (BAS) to support the driver in critical braking manoeuvres. The following Assistance Systems are available as options (standard and optional equipment may vary between markets and versions):

- Intelligent Light System (ILS) with specific lighting functions to match the relevant road and weather conditions,

- Night View Assist Plus with automatic person recognition,

- Speed Limit Assist (standard feature of the COMAND Online option),

- Speed Limit Assist (displays road signs in the instrument cluster),

- ADAPTIVE BRAKE with the functions Hill-Start Assist, priming, brake drying and hold function,

- DISTRONIC PLUS,

- PRE-SAFE Brake with autonomous braking (in conjunction with DISTRONIC PLUS)

- Active Lane Keeping Assist warns the driver as soon as it detects that the car has unintentionally left a recognised marked lane. In addition, it can react with lane-correcting brake application,

- Blind Spot Assist warns the driver when vehicles are detected in the area of poor visibility, the so-called "blind spot". It can counteract a possible collision by specific application of the brakes on one side of the vehicle, if the driver does not react to the warning,

- Park Assist with PARKTRONIC, detects parking spaces and carry out the steering manoeuvres required for the parking process, leaving the driver to operate the brake and accelerator,

- Reversing camera with dynamic guide lines for reversing into narrow parking bays or to aid with the coupling of trailers.

The POST-SAFE functions can activate a variety of systems which can contribute towards avoiding post-accident risks. After a more serious crash, the hazard warning lights are automatically activated to warn surrounding traffic. At the same time, the doors are automatically unlocked, with partial opening of the side windows to ventilate the interior after deployment of the restraint systems.

On detecting a collision, the central control unit switches off the fuel system to reduce the risk of a possible fire. After determining the cylinder positions, the engine management system opens the injection valves of those cylinders which are not under compression and discharges the high-pressure fuel area by direct evacuation of the remaining fuel in the combustion chamber. This reduces the risk of fuel escaping. To avoid fuel losses, all M-Class models are also fitted with cut-resistant fuel lines in all relevant locations. This also helps to reduce the risk of a possible fire breaking out.