Kralev graduated from the University of Architecture, Civil Engineering and Geodesy in 1999, building a business career alongside his subsequent motorsport endeavours. In 2008, he signed a cooperation agreement with the Bulgaria State Tourism Agency to serve as his country's ambassador to the world of motorsport, with his GT3 Ferrari carrying the Bulgarian rose as a tourism promotion.
Kralev began competitive racing in 2003 in the Bulgarian Road Championship, winning the class X3 title in his debut year. He simultaneously claimed the National Off-Road Championship in Bulgaria that same season.
Kralev launched his international career in 2007 in the European Ferrari Challenge series, driving for Team Rosokorso. He recorded two wins in his debut season, at Hockenheimring and Mugello, finishing eleventh overall. In 2008, he moved to Kessel Racing and competed in both the Ferrari Challenge and the FIA GT3 European Championship, partnering first with Dimitar Iliev and later with Niki Cadei. He also contested the German ADAC GT Masters series. Kralev recorded two wins in the Ferrari Challenge in 2008, finishing fifth in the championship, and made a late-season appearance in the International GT Open at Barcelona alongside Matteo Cressoni.
In 2009, Kralev became the first Bulgarian to participate in the 24 Hours of Le Mans, driving the Endurance Asia Team Porsche. The run ended with a gearbox failure at the eighteenth hour, with 186 laps completed. He remains the only Bulgarian driver ever to have started the race. Later that year, Kralev joined the GP2 Asia Series in the 2009-10 season with Trident Racing, completing a full season despite having no prior experience in formula racing.
Kralev moved to the FIA Formula Two Championship for the 2010 season and continued racing in the series through 2011 and 2012. He became the first Bulgarian driver in the championship's history. When the Formula Two Championship disbanded at the end of 2012, Kralev closed this chapter of his career.
Kralev returned to touring car racing in 2014, partially contesting the European Touring Car Cup for Engstler Motorsport with a BMW 320si, finishing tenth with 14 points across three events.
In 2017, he competed in both the FIA European Touring Car Cup and the TCR Italy Touring Car Championship for Kraf Racing with an Audi RS3 LMS. Kraf Racing, a newly formed Bulgarian team, achieved six podiums across the two series despite limited experience. Kralev took two of those podiums in the European Touring Car Cup and four in the TCR Italy series.
Kralev continued in the TCR Italy Championship in 2018 after the European Touring Car Cup folded. He missed the second racing weekend at Paul Ricard due to car damage, but returned for the Misano round — which featured a record 31-car entry — and finished third in the opening race before dropping to ninth in the second after a collision. He wrapped up his active racing career at Misano with that podium finish.
Kralev's career represents a sustained individual effort to carry Bulgarian motorsport into international competition. His record at Le Mans and in Formula Two established benchmarks that no subsequent Bulgarian driver had matched by the time he retired from active racing in 2018.