Marko debuted in sportscar racing in 1966 at Aspern, driving a Triumph Spitfire, and gradually progressed through the European Touring Car Championship. In 1970, driving for Martini Racing, he became a class winner at the 24 Hours of Le Mans.
The following year proved his peak as a driver. Sharing the number 22 Martini Racing Porsche 917K with Dutch driver Gijs van Lennep at the 1971 24 Hours of Le Mans, Marko and van Lennep won the race outright while setting a distance record of 5,335.313 km at an average speed of 222.304 km/h — a record that would stand unbeaten until 2010. The victory came during what was widely regarded as the golden era of the Porsche 917, arguably the most dominant sports car of its generation.
Marko also showed speed in other disciplines that year. At the 1972 Targa Florio, driving an Alfa Romeo 33 around the 72 km Sicilian mountain circuit, he set the fastest lap of the race, catching over two minutes on the leader within two laps before finishing second by 17 seconds with a fastest lap of 33 minutes 41 seconds.
Marko's Formula One career began in 1971 with Jo Bonnier's privateer Ecurie Bonnier outfit at the German Grand Prix, where he drove a McLaren M7C. He did not set a qualifying time and did not start the race. He was then invited by Louis Stanley to join BRM for his home Austrian Grand Prix onwards in 1971, partnering Jo Siffert, Howden Ganley, and Peter Gethin. He drove a spare P153 chassis while teammates used the updated P160.
He retained his BRM seat for 1972. At the French Grand Prix at Clermont-Ferrand, Marko qualified a career-highest sixth place in the newer P160B chassis when a sharp volcanic rock, projected by Ronnie Peterson's March on the ninth lap, pierced his visor and permanently blinded him in his left eye. The injury ended his racing career at 29 years old. He finished his Formula One career with zero championship points from 10 Grands Prix starts, with a best result of eighth place.
Marko transitioned into team and driver management following his retirement from racing. He managed Austrian drivers Gerhard Berger and Karl Wendlinger for several years before founding RSM Marko in 1984, a racing team that competed in the Deutsche Tourenwagen Meisterschaft, Formula Three, and Formula 3000.
From 1999, RSM Marko operated as the Red Bull Junior Team under sponsorship from Red Bull GmbH, and from 2001 it became their formal European driver development programme. Marko joined Red Bull Racing as an adviser when the team debuted in Formula One in 2005, and also served Toro Rosso from its 2006 debut through its subsequent iterations as AlphaTauri and Racing Bulls.
Under Marko's oversight, the Junior Team developed 16 drivers who progressed to Formula One, among them Sebastian Vettel, Daniel Ricciardo, Max Verstappen, Carlos Sainz Jr., and Pierre Gasly. Vettel won four consecutive World Drivers' Championships from 2010 to 2013, becoming the youngest-ever World Champion through the programme. Verstappen then won four consecutive titles from 2021 to 2024. In total, graduates of Marko's programme have won eight combined World Drivers' Championships and 137 Grands Prix. Red Bull also claimed six World Constructors' Championships between 2010 and 2023 during his tenure.
The programme drew criticism for what was described as a cut-throat approach to driver selection and recycling of talent. Marko faced personal controversy in September 2023 when comments about Sergio Pérez's performance were widely interpreted as racially charged; he apologised and the FIA issued a formal reprimand. In early 2024, he was subject to an internal Red Bull investigation over alleged leaking of information related to the Christian Horner misconduct case, but was cleared following talks with Red Bull GmbH.
Marko retired from his management positions at the conclusion of the 2025 Formula One season, with his final graduated driver — Arvid Lindblad — set to debut in 2026. His career represents one of the most unusual in motorsport: a driver whose racing life ended violently and prematurely at 29, followed by four decades shaping Formula One through an unrivalled driver development system.