Rossi grew up in Tavullia after his family relocated there during his childhood. His father, Graziano Rossi, was a former motorcycle racer. Valentino began with kart racing before moving to motorcycles, first competing in the 125cc Italian Sport Production Championship in 1993 on a Cagiva Mito alongside Vittoriano Guareschi.
In 1996, aged 17, Rossi made his Grand Prix debut in the 125cc class. He achieved his first podium at the Austrian Grand Prix, then took both his first pole position and first race victory at the Czech Republic Grand Prix, riding an Aprilia RS125R. He finished the season ninth overall. The following year, riding for the Nastro Azzurro Aprilia team, Rossi dominated the 125cc class, winning 11 of 15 races and claiming his first World Championship with 321 points, celebrating victories with theatrical costumes that earned widespread media attention.
In 1998 Rossi stepped up to the 250cc class on an Aprilia RS250. He won his first 250cc race at the Dutch TT and finished the season as runner-up to Loris Capirossi by 23 points. In 1999, riding as sole official Aprilia GP rider, he dominated the class and clinched the 250cc World Championship in Rio de Janeiro, winning his second title overall.
Rossi moved to the premier 500cc class with Honda in 2000, mentored by retired five-time champion Mick Doohan. After early retirements he scored his first 500cc victory at Donington Park in July, ultimately finishing second in the championship with 209 points.
In 2001 Rossi was dominant, winning 11 races and finishing off the podium only three times. He won the 500cc World Championship with 325 points, 106 ahead of Max Biaggi, claiming his third title overall and the final 500cc championship of the two-stroke era.
When Grand Prix motorcycle racing converted to the four-stroke MotoGP format in 2002, Rossi adapted immediately. He won eight of the first nine races and claimed 11 victories in total, securing the inaugural MotoGP World Championship — his fourth overall — with four rounds remaining. In 2003 he continued his dominance, winning his fifth overall title in Malaysia. His victory at the Australian Grand Prix that year, where despite receiving a ten-second penalty he pulled away by more than fifteen seconds to win, is counted among his finest performances.
At the end of 2003, Rossi parted ways with Honda and signed a two-year contract with Yamaha for a reported sum in excess of US$12 million.
Rossi made the move to Yamaha in 2004 and immediately won the championship, becoming the first rider to win consecutive premier-class titles with different manufacturers. He retained the title in 2005 with eleven victories and 367 points, finishing 147 ahead of runner-up Marco Melandri. His sixth and seventh premier-class championships came with Yamaha in 2008 and 2009, the 2008 title celebrated with a podium shirt reading "Scusate il ritardo" (Sorry for the delay) in Italian.
In 2010 Rossi suffered a displaced compound fracture of his right tibia in practice at Mugello, eliminating any championship challenge. Despite missing four rounds, he returned only 41 days after the accident, eventually finishing third in the championship.
Rossi joined the Ducati factory team in 2011 alongside Nicky Hayden, but endured two difficult winless seasons, finishing seventh (139 points) in 2011 and sixth (163 points) in 2012. He returned to Yamaha in 2013 and rebuilt his form, winning the Dutch TT that year to end a 46-race winless streak.
His closest approach to a tenth world title came in 2015 during his twentieth season in World Championship racing. Rossi led the standings for most of the season but finished five points behind teammate Jorge Lorenzo, a result complicated by a controversial late-season collision with Marc Marquez in Malaysia that resulted in penalty points and a back-of-grid start for the final round. He took three consecutive runner-up positions in 2014, 2015, and 2016.
Rossi's final race victory came at the 2017 Dutch TT, making him at 38 the oldest race winner in the MotoGP era at that time. He joined Petronas Yamaha SRT for 2021, his final season, and retired after the Valencian Grand Prix. His number 46 was officially retired at a ceremony at the 2022 Italian Grand Prix.
Rossi also competed in endurance motorcycle racing during his GP career. At the 2001 Suzuka 8 Hours, riding with Colin Edwards and Manabu Kamada for Team Cabin Honda on a Honda RC51, Rossi won the race, becoming the first Italian rider in history to do so.
Following his MotoGP retirement, Rossi moved to four-wheel sportscar competition with Team WRT, initially driving Audi and then BMW machinery in the GT World Challenge Europe and the FIA World Endurance Championship. He scored his first sportscar race victory at Misano in the GT World Challenge in 2023 and continued to compete at the top level of GT racing through 2026.
Rossi's nine world championships, 89 premier-class victories, and 199 podiums place him among the most decorated athletes in any motorsport discipline. He bridged the final two-stroke era with the MotoGP four-stroke transition, winning championships on both sides of the divide. Through the VR46 Riders Academy, which he founded in 2014 in Tavullia, Rossi developed the next generation of Italian motorcycle racers, with Franco Morbidelli and Francesco Bagnaia — a two-time MotoGP champion — among the graduates. Rossi also owns and manages the VR46 Racing Team, which competes in MotoGP.