O'Ward was born in Monterrey, Mexico, and attended high school in San Antonio, Texas. His surname traces to an Irish great-grandfather, and he identifies as Mexican-American. He began karting in 2005 and remained in the discipline until 2012 before transitioning to open-wheel cars in 2013, competing in Latam Fórmula 2000, Formula Renault 1.6 NEC, and Pacific F2000. In 2014 he raced in the French F4 Championship.
In 2015 O'Ward made his Pro Mazda Championship debut with Team Pelfrey, finishing sixth overall. He returned to Pro Mazda in 2016 and improved to championship runner-up, establishing himself as one of North America's most promising young single-seater talents.
O'Ward joined Andretti Autosport for the 2018 Indy Lights season and dominated the series, winning nine of seventeen races, claiming Rookie of the Year honours, and sealing the drivers championship at the penultimate round in Portland ahead of Colton Herta.
Two weeks after his Indy Lights title, O'Ward made his IndyCar debut at Sonoma Raceway with Harding Racing, qualifying fifth and finishing ninth — matching the best debut result by a Mexican driver in American open-wheel racing. A planned full-time move to IndyCar in 2019 fell through when sponsorship problems forced his release from Harding Steinbrenner Racing. He subsequently joined Carlin on a part-time deal, competing in thirteen races including the Indianapolis 500, though he failed to qualify for the 500. A brief Red Bull Junior Team stint during 2019 saw him contest Super Formula and one Formula 2 round at the Red Bull Ring before being granted an early release when IndyCar opportunities emerged through McLaren.
O'Ward joined Arrow McLaren SP for 2020 and immediately showed his pace, claiming his first IndyCar podium at Road America and finishing the season fourth in the standings. He won the Indianapolis 500 Rookie of the Year award after a sixth-place finish in the rain-delayed race.
The 2021 season elevated O'Ward to title contender status. He took his maiden IndyCar victory at Texas Motor Speedway — becoming the first Mexican driver to win an IndyCar race since Adrian Fernandez in 2004 — and added a second win at Detroit. He led the championship at points before a 14th-place finish at Portland allowed Álex Palou to retake the lead. A controversial final round at Long Beach ended with O'Ward retiring due to a broken driveshaft, leaving him third in the standings behind Palou and Josef Newgarden. He nonetheless claimed the A.J. Foyt Cup as the season's highest-scoring driver on oval courses.
In 2022 O'Ward signed a three-year contract extension with Arrow McLaren, picked up wins at Barber and Iowa, and finished second at the Indianapolis 500 — briefly nosing ahead of Marcus Ericsson for the lead on the final lap before Ericsson held on. O'Ward ended that year seventh in the championship.
The 2023 campaign brought no victories but a career-high count of podiums and top-five finishes, ending with fourth in the standings. In 2024 O'Ward was retrospectively awarded the St. Petersburg victory after race winner Josef Newgarden was penalised for a push-to-pass infringement. He led eleven laps and finished second at that year's Indianapolis 500, then won at Mid-Ohio — becoming the first driver to win a race in IndyCar's hybrid powertrain era — and added a third win at the Milwaukee Mile, recording his first season with more than two victories. He scored his eighth career win at Iowa during his hundredth series start in 2025.
Outside IndyCar, O'Ward demonstrated versatility in endurance racing. In 2017 he co-drove for Performance Tech Motorsports in the IMSA WeatherTech SportsCar Championship's Prototype Challenge class, winning both the 24 Hours of Daytona and the 12 Hours of Sebring to become the youngest driver ever to claim those events, at seventeen years old. He also won the 2017 Prototype Challenge drivers championship alongside James French and the North American Endurance Cup with French and Kyle Masson. He returned to the Daytona 24 Hours in 2022 with DragonSpeed in LMP2, winning the class after co-driver Colton Herta made an overtake in the final eleven minutes.
O'Ward's relationship with McLaren extended beyond IndyCar. Following his 2021 IndyCar win at Texas, McLaren CEO Zak Brown fulfilled a promise of an F1 test: O'Ward drove a McLaren MP4/13 at Laguna Seca in November 2021, posting a lap time faster than his best IndyCar time at the circuit. In December 2021 he tested the McLaren MCL35M in Abu Dhabi, completing 92 laps and finishing fourth fastest. Subsequent tests at Barcelona, the Red Bull Ring, and further Abu Dhabi sessions followed in 2022. He made his Formula One free practice debut at the 2022 Abu Dhabi Grand Prix and has since participated in practice sessions at the Mexico City Grand Prix (2024 and 2025) and the 2025 Abu Dhabi Grand Prix, including the end-of-season young drivers test at Yas Marina. He has continued as McLaren's reserve driver into the 2026 season.
O'Ward is the most successful Mexican racing driver in IndyCar in the modern era, reviving a tradition established by Adrian Fernandez and providing a new generation of Latin American motorsport fans with a credible title contender in North America's premier single-seater championship. His dual presence in IndyCar and the McLaren Formula One programme makes him one of the most prominent drivers in the open-wheel world at large, while his early endurance racing record underlines a rare breadth of talent across racing disciplines.