After placing eighth in his debut in Formula E for Venturi, Dillmann made an impression and was given a full-time drive when Stephane Sarrazin was tempted away to Techeetah, rewarding the team with three more top-10 finishes in the 2016/17 season.

Despite missing out on a full-time drive in the 2017/18 season, the Frenchman filled in for Edoardo Mortara in Berlin while the Swiss driver fulfilled his commitments in the DTM series. Stepping up to his first full-time season in the series, Dillmann joins long-time NIO driver Oliver Turvey behind the wheel of NIO's new Gen2 challenger.

Starting his motorsport career in karting, Dillmann was a regional championship winner before graduating into cars in 2004 with a drive in the Formula Renault 1600. The following season, he moved up into the blue riband Formula Renault 2.0 Eurocup category.

Remaining in Formula Renault until the end of 2006, it wasn't long before Dillmann stepped up to the Red Bull Junior Team, driving in the Formula 3 Euroseries. Stepping into GP3 in 2011, Dillmann made his debut in GP2 during the end-of-year non-championship race at Yas Marina in Abu Dhabi and went on to become a category race winner in 2012. 

Switching to the Formula Renault 3.5 Series in 2015, while also making a handful of outings in the FIA World Endurance Championship and Blancpain Sprint Series, Dillmann secured the FR3.5 title the following season and in August of that year he made his Formula E testing debut.