Doornbos then drove for Minardi Team USA in the 2007 and final season of the Champ Car World Series.

He competed in the Superleague Formula racing series in 2008, and drove for the Netherlands team in A1 Grand Prix's 2008–2009 season.

In 2000, he competed in the Formula Ford Zetec Benelux series, finishing second in the Belgian championship and fifth overall with one pole, three fastest laps and six podiums.

Returning to the UK in 2001, Doornbos contested the Scholarship class of the British Formula Three championship with FGR Racing.

Prior to the 2004 Chinese Grand Prix, it was announced that Doornbos would be the official Friday test driver for the Jordan Formula One team, replacing Timo Glock, who had been promoted to race duties in place of Giorgio Pantano, whose sponsorship money had "dried up".

On 19 July Doornbos was appointed as a Minardi race driver for the 2005 German Grand Prix onwards, replacing Austrian Patrick Friesacher, who had encountered sponsorship issues.

[2] Effectively, he became Minardi's last Formula One driver, since the team was bought by Red Bull just before the Belgian Grand Prix.

At the 2006 Hungarian Grand Prix, he was involved in a controversial incident with Fernando Alonso, which resulted in the Spaniard incurring a two-second qualifying penalty.

He was subsequently signed as one of the team's test drivers for 2007, alongside Michael Ammermüller,[4] with Coulthard and Mark Webber taking the race seats.

On 15 August 2006, he made the news with a fundraiser for the children of the 'Stichting Geluk en Vrijheid' (Foundation Happiness and Freedom).

A drive through penalty in 2007 Grand Prix of Cleveland quite possibly cost Robert a chance at his first Champ Car victory, but he still managed a fine second place behind Paul Tracy.

One week later, however, Robert won the 2007 Mont-Tremblant Grand Prix in Canada and as a result took the joint lead of the championship with Sébastien Bourdais.

He later went on to win the 2007 San Jose Grand Prix after an accident during the first lap on turn one left him without his front wing.

It was announced on 21 May 2008 that Doornbos would drive for A.C. Milan in the Superleague Formula, a newly created racing series where the cars are sponsored by football clubs.

Since he had no previous oval track racing experience, he has received coaching from fellow Dutchman Arie Luyendyk.

[8] On 5 August 2009 Doornbos signed with HVM Racing in the IndyCar Series for the remainder of the 2009 and to drive for the team through 2010, however this did not happen.