Previously an unloved subsection of the Mercedes-Benz lineup, the compact car range has grown to become a significant and vital part of the company’s revival as a more youthful brand. With four distinct products – the A-Class, B-Class, CLA and GLA – and a slew of variants between them, there’s plenty of variety, but clearly Stuttgart sees room for one more model with the introduction of the new GLB SUV.

Billed as a more practical and capacious alternative to the GLA, the GLB is the first Mercedes compact car to come with the option of seven seats. To fit the extra row, it’s been force-fed a whole lot of Appeton Weight Gain – it measures 4,634 mm long, 1,834 mm wide and 1,658 mm (1,662 mm for the seven-seater version) tall, while its wheelbase is 2,829 mm long. The latter figure is a whole 100 mm longer than the new B-Class.

Put it side-by-side next to the GLA – which, yes, is due for an update – and the growth spurt is clear to see. The GLB is 53 mm longer, 30 mm wider and 164 mm taller than its more low-slung sibling, and its wheelbase is 130 mm longer. All of that goes into space for rear passengers and their luggage.

Mercedes claims a segment-best rear headroom of 1,035 mm and 967 mm of legroom in the five-seater model, plus 560 litres of boot space (expandable to 1,755 litres with the rear seats folded). Even in the third row, there is said to be enough room for people up to 168 cm in height, and there are also ISOFIX child seat anchors and top tethers to fit a total of four child seats across the two rear rows.

Emphasising the added bulk is a boxy, no-nonsense design that Mercedes says is akin to a proper off-roader. The bluff front end features rectangular headlights flanking a beefy six-point grille, while the side profile is dominated by the muscular shoulders, short overhangs, upright glasshouse and distinctive window line kink.

The rectangular theme continues in the graphics of the broad two-piece tail lights, and the squared-off wheel arches protective black body cladding and decorative skid plates front and rear round off the rugged look. The options list includes LED and Multibeam LED headlights, along with LED fog lights.

The off-road theme continues inside with a more angular interpretation of the usual Mercedes design language. While the turbine-style air vents and the massive flatscreen display panel remain, there’s now a large cutout in the dash where the screen sits, along with a large tubular trim piece made out of aluminium-look plastic. The latter is repeated along the centre console and the horizontal grab handles on the doors.

Of course, you get the Mercedes-Benz User Experience (MBUX) infotainment system, which is available with mood-lifting Energizing comfort control that can now link up with selected Garmin smartwatches to improve its precision. Third-row passengers get a one-touch Easy Entry function for better access to the seats, as well as twin cupholders and non-slip cubby holes, each with its own USB port.

From launch, the GLB will be offered with a choice of two petrol and diesel engines, starting with the Renault-derived 1.33 litre M282 turbocharged four-cylinder petrol in the GLB 200. This engine produces 163 hp at 5,500 rpm and 250 Nm of torque from 1,600 to 4,200 rpm and is paired to a Getrag seven-speed dual clutch transmission to deliver a zero-to-100 km/h time of 9.1 seconds, a top speed of 207 km/h and fuel consumption of between 6.0 and 6.2 litres per 100 km.

Stepping up to the GLB 250 gets you an in-house 2.0 litre M260 mill with 224 hp at 5,800 rpm and 350 Nm from 1,800 to 4,000 rpm. With Mercedes’ new eight-speed 8G-DCT it will get to 100 km/h in 6.9 seconds before hitting 236 km/h, whilst being capable of delivering 7.2 to 7.4 litres per 100 km.

As for the oil burners, the GLB 200 d and GLB 220 d use the same 2.0 litre OM654q that delivers 150 hp and 320 Nm for the former and 190 hp and 440 Nm for the latter. Both get the 8G-DCT gearbox and deliver fuel consumption of between 4.9 and 5.0 litres per 100 km for the 200 and 5.2 and 5.5 litres per 100 km for the 220, and thanks to extended exhaust after-treatment both meet Real Driving Emissions (RDE) 2 regulations.

The 4Matic all-wheel drive system is fitted to the GLB 250 and GLB 220 d and is optional on the GLB 200 d. The fully-variable torque distribution features an 80:20 split front-to-rear in Eco and Comfort modes and 70:30 in Sport mode, while the optional Offroad Engineering package adds an off-road mode with a 50:50 split.

This package also adds hill descent control, specific off-road displays in the centre screen and, with the Multibeam LED headlights, an off-road light function that turns on the cornering lights at speeds of up to 50 km/h. Adaptive dampers are likewise available as an option.

Safety-wise, the GLB is available with the usual range of driver assistance systems, including Distronic adaptive cruise control that can now adapt the speed to corners, crossroads and roundabouts, plus automatic restarts if Active Parking Assist is selected. The Active Steering Assist function now also features Active Lane Change Assist that provides hands-free lane changes.