Hegewald began racing in professional karting and spent three seasons at that level before transitioning to circuit racing. A notable early result came at the 2002 Junior Monaco Kart Cup at ICA Junior level, where he finished fifth in a field that also included future Formula One drivers Jules Bianchi and Sébastien Buemi, as well as Formula Three Euroseries competitors Alexander Sims, Jean Karl Vernay, and Stefano Coletti.
Hegewald stepped up to single-seater competition in 2005, competing concurrently in the Formula BMW ADAC series in Germany and the Formula BMW USA series. He finished 20th in the German championship with six points, and 15th in the American series with 22 points and two pole positions, including a pole at the Canadian Grand Prix support race in Montréal.
In 2006, his results showed modest improvement in the German series, where he collected 29 points across 18 races to finish 13th. He again made four appearances in the American series, scoring 23 points and finishing 14th in that championship.
For 2007, Hegewald joined the Oschersleben-based Motorsport Arena team for a dual campaign in the Formula Renault 2.0 Northern European Cup and the Formula Renault Eurocup. His Eurocup performances were inconsistent, but in the Northern European Cup he mounted a serious title challenge, finishing as runner-up to Frank Kechele with three victories and ten podiums despite a 79-point deficit at the end.
The team was renamed Motopark Academy for 2008, and Hegewald continued in both championships. His Eurocup results improved significantly, earning fifth place in the standings with two podiums. However, he was regularly outpaced by teammate Valtteri Bottas, who went on to win the Eurocup after a hard-fought battle with Daniel Ricciardo, Andrea Caldarelli, and Roberto Merhi. In the Northern European Cup that year, Hegewald managed only one victory from 14 races and slipped to third in the championship, with Bottas again dominant and António Félix da Costa also finishing ahead of him. Motopark Academy's strength was evident in locking out the top four positions in the NEC, with Johan Jokinen also finishing fourth.
In 2009, Hegewald made a one-off appearance in the Formula Renault 3.5 Series at its second event of the season, substituting for Mihai Marinescu at the Interwetten team.
After competing in Formula Palmer Audi over the off-season, Hegewald signed for the relaunched FIA Formula Two Championship in 2009, driving car number 8. He produced his finest professional performance at Spa-Francorchamps, where he swept both pole positions, both fastest laps, and both race victories in a single weekend — a dominant display that stood as a highlight of the series that year. He ended the championship in sixth place overall.
Hegewald returned to the FIA Formula Two Championship in 2011 following his season in the GP3 Series.
For 2010, Hegewald moved to the inaugural season of the GP3 Series, joining RSC Mücke Motorsport alongside Nigel Melker and Renger van der Zande. The GP3 Series had been launched that year as a new support category for the Formula One World Championship, and Hegewald was among the first wave of drivers to compete in the championship.
Hegewald's career traced a path through the European junior single-seater ladder during a period when future Formula One regulars such as Valtteri Bottas, Daniel Ricciardo, and Sébastien Buemi were also establishing themselves. Racing alongside and against this generation, Hegewald demonstrated competitive pace at the Formula Renault and Formula Two levels without ultimately making the step to the highest tiers of the sport. His commanding double-victory at Spa in 2009 remains the defining result of his career.