A top rider of the Italian Minimoto Championship from 1996 to 2000, Marco Simoncelli moved to 125cc bikes after taking two consecutive titles in the aforementioned discipline. After a promising first season in the 125 Honda Trophy, Simoncelli took the European 125cc title in 2002 and had a first taste of Grand Prix racing the same year.
In 2003 he undertook his first full season in the World Championship with the Matteoni Racing team. A consistent point-scorer in his rookie season, he moved to the Rauch Bravo team in 2004 and scored his first Grand Prix win at a rain-soaked Jerez, but could only manage an eleventh placed finish overall.
Another 125cc campaign in 2005, with the Nocable.it Race team, was completed with an improvement in the final standings in fifth place, giving Simoncelli the opportunity to leap into the quarter-litre category. A steady season saw the Italian achieve 10th position in the championship representing Metis Gilera, with whom he continued in 2007 and 2008.
In 2008 Simoncelli achieved his first race victories in the 250cc class, his maiden triumph coming at his home race in Mugello, and was involved in some breathtaking battles with his rivals over the course of the year. Emerging as the standout rider in the class, Gilera provided their newest star with a top-of-the-range RSA machine for the final races of the season.
The Italian secured his fifth win of the year at Phillip Island early in October and clinched the title with third place at Malaysia at the penultimate round of the year. He previously rode a Gilera in the 250cc World Championship, and has previously in the 125cc class. He has five race wins in the 250cc class, and two in the 125cc class.
He made a one-off appearance for Aprilia in the World Superbike round at Imola. He qualified on the second row and was one of three riders to crash out of race one at Tosa while running fifth, before fighting through to third in race two, making a forceful move to overtake team-mate Max Biaggi to get onto the podium.
On 25 June 2009, it was confirmed that Simoncelli would move up to premier class racing for 2010 MotoGP championship after agreeing to ride with the San Carlo Gresini Honda team.
Simoncelli died after an accident during the 2011 Malaysian motorcycle Grand Prix on 23 October 2011.