The W03 was launched on 21 February 2012, ahead of the second pre-season test at the Circuit de Catalunya in Barcelona. Mercedes used the outgoing MGP W02 at the first test in Jerez de la Frontera to evaluate the 2012 specification of Pirelli tyres before the new car was ready. The W03 completed a shakedown at Silverstone on 16 February and conducted a private test at Barcelona on 19 February — permitted under sporting regulations as the team had attended only three of the four test days at Jerez.
The W03 was introduced at the season-opening Australian Grand Prix with what was described as a radical front wing concept. The system channelled air through the car via ducts exposed when the drag reduction system (DRS) flap opened in the rear wing, creating an effect over the front wing that reduced downforce and drag on long straights — broadly similar in concept to the F-duct system developed by McLaren in 2010.
On the Thursday before the Australian Grand Prix, the FIA's technical delegate Charlie Whiting declared the system legal. However, Red Bull Racing and Lotus F1 challenged the ruling ahead of final practice, citing violations of Articles 3.15 and 3.18 governing driver-operated aerodynamic devices. The FIA rejected these claims in Malaysia, and when Lotus filed a formal protest at the Chinese Grand Prix, the stewards dismissed it unanimously. The stewards ruled that the Mercedes design was consistent with the stated purpose of DRS — improving overtaking — and confirmed the FIA had pre-cleared the concept under Articles 2.4 and 2.5 before the season began. Lotus did not appeal.
The W03 delivered the breakthrough result Mercedes had been building toward. At the Chinese Grand Prix, Nico Rosberg took pole position and converted it into victory — Mercedes' first Formula One win as a constructor since Juan Manuel Fangio won the 1955 Italian Grand Prix. The car finished the season with three podium finishes in total and that single victory.
Schumacher reached the podium for the last time in his Formula One career at the European Grand Prix in Valencia. The team finished fifth in the World Constructors' Championship with 142 points, a drop of 23 points compared to the W02's total, though that figure was partially shaped by the competitive environment of the field in 2012. The result also represented, until 2024, the last time Mercedes finished behind one of their customer teams in the Constructors' standings.
At the Brazilian Grand Prix, both W03 chassis carried a special farewell logo to mark Schumacher's retirement from Formula One at the end of the season.
The W03 season was a pivotal moment in Mercedes' trajectory. The Chinese Grand Prix victory ended a 57-year winless drought for the marque and demonstrated that the substantial investment Mercedes had made since acquiring Brawn GP was beginning to pay competitive dividends. Although the car itself was not consistently at the front, it laid the technical and organisational groundwork for the dominant W05 and subsequent machines. The season also marked the close of Michael Schumacher's career: his final podium in Valencia was the last competitive result he would record.
At the 2014 Goodwood Festival of Speed, Lewis Hamilton drove a W03 dressed in the livery of the 2014 championship-winning W05.