In 1983 Bellof joined the Rothmans-backed Porsche factory team for the World Endurance Championship driving a Porsche 956 alongside Derek Bell. Bellof and Bell won first time at the 1000 km Silverstone, beating Bob Wollek and Stefan Johansson by almost a minute, having taken the lead at half-distance, completing the race's duration at an average speed of . Bellof's pole time for the race – 1 minute, 13.15 seconds – would have put him twelfth on the grid for the later in the year. The next race on the calendar was the 1000 km Nürburgring in which Bellof rewrote several records at the Nordschleife. His pole time for that race of 6 minutes, 11.13 seconds is unofficially the fastest lap ever driven on the Nürburgring Nordschleife in its current configuration, taking pole position by five seconds, at an average speed of . Bellof also set the fastest lap during the race, with a lap time of 6 minutes, 25.91 seconds, which remains the official Nordschleife lap record for all cars. Two laps after setting the race record, on lap 20, Bellof's 956 – chassis 956-007 – flipped out of the race at the Pflanzgarten. Bellof added two more wins later in the season at Kyalami and at Fuji, as he ended the season in fourth position. He also added a win in the non-championship Norisring Trophäe race.