Sofuoglu began his competitive career in Turkish domestic championships, winning Class B of the Turkish Supersport Championship in 2000 and the German Yamaha R6 Cup in 2002. He moved into the European Superstock Championship, finishing second and third across two seasons before stepping up to the Supersport World Championship. He made his first WSS appearances in 2003 and joined the class full-time in 2006.
Sofuoglu's breakthrough season came in 2007 when he dominated the Supersport World Championship with Ten Kate Honda. He won five of the first eight races, setting a record for most wins in a single season at that point. His victories included a charge from sixth to first place in two laps at Monza and a win on his first visit to a wet Donington Park. He also triumphed at Losail, in Spain, and at Assen. Sofuoglu clinched the title with three races remaining, finishing second at Brands Hatch to become Turkey's first major motorsport world champion.
For the 2008 season Sofuoglu moved up to the Superbike World Championship with a third Ten Kate Honda CBR1000RR in a junior capacity, though the campaign produced limited results. He returned to the Supersport class with Ten Kate for 2009, finishing behind Cal Crutchlow and Eugene Laverty. In 2010 he reclaimed the Supersport title in a three-way battle with Laverty and Joan Lascorz, finishing on the podium in every race.
Towards the end of the 2010 season Sofuoglu made his Moto2 debut at the Portuguese Grand Prix with the Technomag-CIP team, replacing Shoya Tomizawa, who had died following an incident at Misano. Despite having no prior dry laps on the bike, Sofuoglu qualified on the front row (after rain cancelled normal qualifying) and led for much of the race before finishing fifth. He stayed with the team for the full 2011 season, with his best result being second place at Assen.
Racing with Kawasaki in 2012, Sofuoglu secured his third Supersport world title at the Portuguese Grand Prix, the penultimate round of the season. After a stint with the Indian Mahi Team in 2013, he went on to add two further championships in 2015 and 2016, cementing his status as the class's all-time record holder with five titles.
Sofuoglu's later career was marked by a series of significant injuries. In early 2017 he broke a finger bone during training and required multiple operations, forcing him to miss the opening rounds of the season. On 30 September 2017 he suffered a triple pelvic fracture in a crash during the Superpole session at Magny-Cours, France, and was airlifted to Istanbul for treatment. Despite a projected twelve-week recovery, he returned in just five weeks to compete at the final round in Qatar, finishing third and securing second place in the championship standings.
In 2018 Sofuoglu sustained further injuries in a crash at Phillip Island, Australia. He announced his retirement from racing in May 2018 ahead of the Imola round, though he made a brief appearance there, qualifying third before withdrawing from the race after the sighting lap.
Sofuoglu was elected to the Turkish Grand National Assembly in June 2018 as a Justice and Development Party (AK Party) representative for Sakarya Province. On the parliament's opening day, 4 July 2018, he arrived driving a Lamborghini Aventador, an act that drew public commentary regarding the display of wealth by an elected official. Sofuoglu stated that he donates his parliamentary salary to charity.
As a five-time Supersport World Champion, Sofuoglu holds more titles in the class than any other rider in history. His 2007 championship made him Turkey's first major motorsport world title holder, and his record of consistency across multiple manufacturers — Ten Kate Honda, Kawasaki, and others — demonstrated versatility across more than a decade at the top of the class. His career win record in the Supersport World Championship stands among the highest ever accumulated.
Sofuoglu is the third of five children of Irfan Basri Sofuoglu, a motorcycle repairman, and his wife Nurhayat. Two of his brothers, who were also local motorcycle racers, died in accidents: his eldest brother Bahattin, a domestic Turkish motorsport champion, in a road traffic accident in 2002, and his brother Sinan during a training incident at the Izmit Korfez Circuit in May 2008. Sofuoglu speaks German, French, English, and Turkish. He married Julia Looman in September 2014. His racing number 54 derives from the license plate number of Sakarya Province, his home region.