The 2005 Formula 3 Euro Series season was the third championship year of Europe's premier Formula Three series. The championship consisted of ten rounds – each with two races – held at a variety of European circuits. Each weekend consisted of one 60-minute practice session and two 30-minute qualifying sessions (one at Monaco), followed by one c.110 km race and one c.80 km race. Each qualifying session awarded one bonus point for pole position and each race awarded points for the top eight finishers, with ten points per win. Lewis Hamilton dominated the season, winning 15 of the 20 races and scoring nearly twice as many points as his nearest rival, team-mate Adrian Sutil. As of now, six drivers (Hamilton, Sutil, Sebastian Vettel, Paul di Resta, Lucas di Grassi, and Giedo van der Garde) have competed in Formula One.
The 2005 calendar included events at the historic circuits of Pau (France), Spa-Fracorchamps (Belgium), Zandvoort (Netherlands) and Monaco. Monaco has a long tradition of Formula 3 events, but this was the first since 1997. The debut of a new street circuit in the French town of Avignon was to take place in September, but the plans fell through and its date was given to the Lausitzring.
Thirteen countries were represented in the drivers' entry list, which included drivers from Argentina, the USA and the Czech Republic for the first time. There were teams from France, Germany, Britain, Austria, Italy, Netherlands, Luxembourg and the Czech Republic.
After a promising debut season with Manor Motorsport that ended with a win in the non-championship Bahrain F3 Superprix, and a contract with ASM for 2005, Lewis Hamilton was regarded as the championship favourite. He exceeded expectations by winning 15 races from 20 starts, securing 13 pole positions, posting ten fastest race laps, and scoring nearly twice as many points as his nearest rival, team-mate Adrian Sutil. Lucas di Grassi made a full-time return to the series (he entered two rounds in 2003) and finished in 3rd place overall, with one win. The highest-placed rookie was the then-reigning Formula BMW Germany champion Sebastian Vettel, who was classified 5th overall with six podium finishes. He was beaten to 4th place by Franck Perera's more consistent points finishes.
In the Teams’ Championship, ASM Formule 3 retained the title that it had secured in 2004, with Signature in a distant second place. Third place was taken by Prema Powerteam, which had won the Euro Series' first teams' title in 2003. Manor Motorsport was classified 4th overall, as it continued to improve its form against rivals with more experience in Europe. At this time, the Spiess-Opel engine was still numerically dominant, but won on only two occasions. HWA-Mercedes had begun to gain the upper hand in 2004 (with 13 wins from 20 races), and increased its development effort to win 18 races in 2005.
Maximilian Götz left HBR Motorsport after four rounds, to be replaced by Danny Watts, making his Euro Series debut. Watts was able to stay for only one round, and the HBR line-up was subsequently reduced to two cars. Götz returned at the final round as a substitute for Adrian Sutil at ASM. Sutil's absence was due to commitments in the A1 Grand Prix series. Five drivers shared Team Midland's #19 car. Richard Antinucci competed in the first four rounds, before Nico Verdonck of Belgium replaced him at Oschersleben and the Norisring. He in turn was replaced by three British drivers, all Euro Series rookies: Stephen Jelley at the Nürburgring, Rob Austin at the Lausitzring and Zandvoort, and Ben Clucas in the final round of the season at Hockenheim. A number of registered drivers failed to complete the season, including Paulo Montin, who made only two starts with Ombra Racing; and Julia Kuhn, who made two starts in round 1 and attempted (but failed) to qualify for the first race of round 10. RZ Racing left the series after round 9 at Oschersleben.