The GP2 Series was created to replace International Formula 3000 as the primary feeder series to Formula One. The 2005 season was technically the thirty-ninth season of the second-tier Formula One feeder championship under its accumulated history, but the first under the GP2 name. All teams competed in the standardised Dallara GP2/05 chassis, powered by Renault-badged 4.0-litre naturally-aspirated Mecachrome V8 engines. Car numbers for the inaugural season were allocated at a pre-season test at Circuit Paul Ricard, where the fastest driver earned number 1.
The reigning Formula 3000 champion Vitantonio Liuzzi was absent, having graduated directly to Formula One with Red Bull Racing. Two former Formula One drivers joined the grid: Gianmaria Bruni, who had raced for Minardi in 2004, joined Coloni Motorsport, while Giorgio Pantano, formerly of Jordan, drove for Super Nova International.
The season opened at Imola in April 2005, where concerns about the start procedure led organisers to use rolling starts for both races despite dry conditions. Nicolas Lapierre had taken pole position but retired before the race began with a mechanical problem. His team-mate Heikki Kovalainen won the opening feature race, launching a strong early-season campaign. The first four races produced four different winners from four different teams, illustrating the competitive depth of the new series.
A rule adjustment after the opening weekend stipulated that points for fastest lap would only be awarded if the driver was classified as a finisher, closing a loophole exploited at Imola where Lapierre set a fastest lap on minimal fuel before retiring.
At the Circuit de Barcelona-Catalunya, standing starts were finally introduced. Bruni took the feature race victory and José María López won the sprint, continuing the pattern of varied results. Adam Carroll became the first driver to take two victories in the series after winning at Monaco, where a single race was held rather than the usual feature-sprint format.
The sprint race at the Nürburgring was extended from 80 to 120 kilometres, and Monegasque driver Clivio Piccione claimed an impressive victory there. Kovalainen built a championship lead through the first half of the season, winning three of the first five feature races, but a tactical shift came at Magny-Cours when ART Grand Prix found a new level of pace. Despite losing the feature race through tactical errors, Nico Rosberg gave ART their first victory in the sprint. He followed that with wins in the next two feature races to begin clawing back Kovalainen's advantage.
At the Hungaroring, the ART cars were disqualified from qualifying for an illegal steering rack position and were sent to the back of the grid, yet still scored points in the feature race and finished one-two in the sprint, where Alexandre Prémat claimed his first victory. Neel Jani won the feature race. Prémat also won at Istanbul in a race that exposed the championship battle's volatility, as both Kovalainen and Rosberg failed to score points there. In the sprint race at Istanbul, Kovalainen climbed from tenth to first after a well-timed tyre stop.
At Monza, Kovalainen and Jani each won a race while Rosberg consolidated with two second-place finishes and two fastest laps. Nelson Piquet Jr. won the feature race at Spa-Francorchamps as Rosberg took the championship lead after Kovalainen spun out on the final lap while fighting for position. The sprint at Spa was stopped early following multiple accidents involving Ernesto Viso, Hiroki Yoshimoto, and Jani, with only half-points awarded.
The championship concluded at the Bahrain International Circuit, the only event that season not held in support of a Formula One race. Rosberg entered the finale leading Kovalainen by three points. He took pole position, won the feature race with Kovalainen finishing third, and then also won the sprint race — becoming the first driver in the series to win both races at the same event. His dominant final weekend confirmed the title beyond doubt.
Feature races awarded points to the top eight finishers, while sprint races paid out to the top six. The pole-sitter in the feature race received two bonus points, and two additional points went to the drivers who set fastest laps in both the feature and sprint races. Drivers were required to complete 90 percent of the race distance to remain classified.
Several drivers who would go on to significant Formula One careers competed in the inaugural GP2 season. Nico Rosberg went on to win the 2016 Formula One World Championship. Heikki Kovalainen reached Formula One the following year and raced for McLaren in 2008. Nelson Piquet Jr. later contested the 2008 and 2009 Formula One seasons. Scott Speed joined Scuderia Toro Rosso in 2006. The season represented a significant gathering of Europe's emerging single-seater talent under a unified, cost-controlled format that would define the pathway to Formula One for the following decade.
The 2005 season comprised 23 races at 12 circuits, with race weekends held at Imola, Barcelona, Monaco, the Nürburgring, Magny-Cours, the Hungaroring, Istanbul Park, Monza, Spa-Francorchamps, and Bahrain. The season ran from 23 April to 25 September 2005.