Ingrassia began his professional life as a sales representative for Coca-Cola before discovering rallying and making his debut as a co-driver in 2002 at France's Critérium des Cévennes. He spent several years gaining experience in regional French rallies before competing in the Peugeot 206 Cup in 2004.
The turning point came at the end of 2005, when Ingrassia attended the Rallye Jeunes selection organised by the French Federation and encountered Sébastien Ogier, that year's winner. The two teamed up for the 2006 season in the Rallye Jeunes FFSA team, with Ingrassia co-driving Ogier through his first rallies and first wins in the Peugeot 206 Cup. Over the following seasons they honed their craft in regional and national events before stepping onto the international stage.
In 2008, Ingrassia reached world-level competition through the Junior World Rally Championship with the FFSA French team. He and Ogier won three of the six season rallies and claimed the JWRC title, establishing themselves as the new generation of French rallying talent. They contested only a single JWRC season before moving directly into the full WRC.
The pair joined the Citroën Junior Team in 2009, with Ingrassia scoring his first WRC podium alongside Ogier at the Acropolis Rally. Their first outright WRC win followed in 2010 in Portugal; a second victory came that year in Japan. Promoted to the official Citroën Total World Rally Team for the gravel rounds of 2010, they demonstrated pace matching the factory hierarchy. In 2011, operating full-time as Citroën factory drivers, Ogier and Ingrassia matched team-mates Loeb and Elena with five rally wins apiece, though team orders at the season's end favoured the established Loeb pairing.
After leaving Citroën, Ingrassia and Ogier chose to join Volkswagen Motorsport for 2012. Rather than contest that WRC season in an undeveloped car, they sat out the championship in order to develop the new Polo R WRC, competing in the meantime at the wheel of a Skoda Fabia S2000.
The Polo was ready for the 2013 Rally Monte Carlo, and the crew won on its very first competitive stage. They went on to record nine victories, 111 stage wins, and 290 championship points — a points-in-a-season record. The co-drivers' title was secured on home soil at Rallye France, with Volkswagen also claiming the manufacturers' crown. In 2014, further wins at Monte Carlo, Mexico, Portugal, Italy, Poland, Australia, Spain, and Wales delivered a second title; Ingrassia became the first French co-driver to win two WRC championships. By this point he was ranked, with 24 victories across five seasons, as the third most successful co-driver in WRC history at the time.
The crew won again in 2015 and 2016, making four consecutive titles with Volkswagen before the manufacturer's surprise withdrawal from the series at the end of 2016.
Ogier and Ingrassia joined the privateer M-Sport World Rally Team for 2017, winning Rallye Monte-Carlo on their debut and taking the championship title at the penultimate round, edging Thierry Neuville and Ott Tänak. In 2018 they recorded a fifth consecutive Monte Carlo win — a record for that event — plus victories in Mexico and France. Though they trailed Neuville and Tänak deep into the season, a win in Wales Rally GB revived their campaign and they eventually claimed a sixth title in Australia.
Seven years after their original Citroën partnership ended, Ogier and Ingrassia returned to the marque for 2019. They opened the season with a sixth consecutive Monte Carlo win — the narrowest in the rally's history, with a margin of just 2.2 seconds over Thierry Neuville and Nicolas Gilsoul. Additional wins came in Mexico and Turkey, but a mixed season with the C3 WRC left them third in the championship.
Signing with Toyota Gazoo Racing for 2020, the pair won the shortened season's closing Monza Rally and took their seventh world title. For their final season in 2021 they sustained strong form in the first half, winning four of the first six rallies including a first appearance at the revived Safari Rally. On 7 October 2021 Ingrassia announced his retirement from co-driving at the end of the season, closing a partnership of sixteen seasons with Ogier.
Ingrassia's eight WRC co-drivers' championships with three different manufacturers stands as one of the sport's most exceptional records. His most prolific statistical season was 2013, during which he recorded a stage-win rate of 46.25 percent — 111 wins from 240 stages — and led stages for 62.92 percent of the season. His career total of 2,511 WRC points set a record for co-drivers.
Following retirement, Ingrassia worked as a television presenter and commentator for motorsport programmes. In 2025 he co-founded the World Rally Drivers Alliance, a trade union of professional rally crew members created to represent the concerns of drivers and co-drivers within the WRC, particularly in response to FIA policies regarding conduct during sanctioned events.