Monteiro began racing in the 1997 French Porsche Carrera Cup, taking five wins, five pole positions, and the B-class championship. He moved to French Formula Three in 1998 and steadily improved, finishing second in the championship in both 2000 and 2001, the latter campaign yielding six pole positions and four wins. In 2002 he stepped up to International Formula 3000 before spending 2003 in the Champ Car World Series with Fittipaldi Dingman Racing, achieving a front row start in Mexico City and finishing 15th overall. In 2004 he raced in the World Series by Nissan with Carlin Motorsport, finishing runner-up to Heikki Kovalainen and earning Autosport magazine's ranking in the top ten drivers from Formula One feeder series.
Monteiro joined Jordan Grand Prix — by then under Midland Group ownership — for 2005 alongside Indian driver Narain Karthikeyan. The season's defining moment came at the United States Grand Prix. After all seven Michelin-shod teams withdrew from the race due to tyre safety concerns following a tyre failure, only the three Bridgestone teams took the start. Monteiro finished third from a field of six cars, becoming the first Portuguese driver to stand on a Formula One podium. He finished the podium ceremony alone after the Ferrari drivers quickly departed, receiving applause from the attending fans. The result earned seven championship points — a record for a Portuguese Formula One driver, previously held by Pedro Lamy with one point.
Monteiro also became notable during the 2005 season for completing consecutive race finishes as a rookie, breaking the record previously shared by Jackie Stewart (1965) and Olivier Panis (1994), who had each finished their first six races. Monteiro's run extended that streak until the 2013 season, when Max Chilton finished all nineteen races. A notable footnote from the Turkish Grand Prix: Monteiro suffered severe toothache before the race; team principal Colin Kolles, a qualified dentist, performed emergency root canal surgery to allow him to start. He finished 15th.
Monteiro scored one further championship point at the Belgian Grand Prix to close the season with seven points total.
Jordan was rebranded as Midland for 2006, and Monteiro was retained alongside Christijan Albers. The Midland M16 was uncompetitive throughout the season; neither driver scored points. Monteiro retired from six of the eighteen races, with a ninth place at the Hungarian Grand Prix representing his season's best finish. At year's end he was replaced by Adrian Sutil when the team was again renamed, this time to Spyker.
Monteiro joined the SEAT Sport team in the World Touring Car Championship for 2007, taking three podiums and a pole in his debut season. Driving the SEAT León TDi in 2008, he took his first WTCC victories at Puebla in Mexico and at Estoril in his home country of Portugal. He remained with SEAT-backed operations through the manufacturer's formal withdrawal and into the 2010 season, when he won at Portimão and Valencia to finish fifth in the championship — his strongest result to that point.
Monteiro switched to Honda in 2012, joining the new Honda Racing Team JAS outfit. He won his first race with Honda at Shanghai in 2013, contributed to Honda winning the manufacturers' world championship that year, and added victories in Russia and Japan in 2015. The 2016 season was his finest: wins in Slovakia and Portugal, five further podiums, and a third-place championship finish, the highest of his career.
In 2017, Monteiro led the championship standings after twelve rounds when he was seriously injured in a testing crash at Barcelona caused by brake failure. He missed the remainder of the season. He returned to competition at Suzuka in November 2018 for the penultimate WTCR round, greeted by applause from fellow drivers as he went out first for practice. A full-season return in 2019 brought his first World Touring Car win since the accident, taken at his home race in Portugal. He competed in the series through its final season in 2022.
Monteiro also won the Nürburgring 24 Hours in the TCR class in both 2019 and 2020.
Monteiro purchased the GP2 team BCN Competición in November 2008, renaming it Ocean Racing Technology. Under his ownership the team competed in GP2, the GP2 Asia Series, and GP3 before withdrawing due to funding constraints at the end of 2012. He serves as manager for fellow Portuguese driver António Félix da Costa, who won the Formula E World Championship in the 2019–20 season, and also manages his son Noah Monteiro's emerging career.
Monteiro's Formula One career was modest in scope but historically significant for Portuguese motorsport: his 2005 United States Grand Prix podium remains the best result achieved by any Portuguese driver in Formula One, and his seven championship points surpassed the previous national record. His long WTCC and WTCR career demonstrated sustained competitiveness through multiple manufacturer programmes and a serious recovery from career-threatening injury in 2017. Outside the cockpit, his team management and ownership work extended his contribution to motorsport beyond driving.