Pieter Braun has been competing in international competitions since 2010, although at that time he was not yet specialized in all-round competitions. In 2012 he qualified for the U20 World Championships in Barcelona. There he was 16th with 7055 points. A year later he scored more than 500 points in the older age group at the U23 European Championships than a year earlier at the Junior World Championships, with which he finished 11th.
In the spring of 2015, Braun took part in his first international adult competition at the European Indoor Championships in Prague. With 4832 points, he took eleventh place. In the summer he celebrated his greatest sporting success to date by winning the U23 European Championships in Tallinn. One month later he was able to approximately confirm the number of points of his title win at the World Championships in Beijing, with which he finished twelfth there. He had to give up the decathlon at the 2016 Olympic Games in Rio de Janeiro after the first day of competition. Before that, he finished seventh at the European Championships in his native Netherlands.
At the World Championships in London 2017, he stayed below 8,000 points and did not get beyond 16th place. In May of the next season at Götzis' all-rounder meeting, he set his current best of 8342 points. For a few months he took seventh place at the European Championships in Berlin, just like two years earlier. He also achieved this placement at the 2019 World Championships in Doha.