In 2007, Chagaev defeated then-unbeaten Nikolai Valuev to win his first WBA heavyweight title and would make two successful defences. Due to injuries and being unable to grant Valuev a rematch in 2009, the WBA stripped Chagaev of the title. He went on to suffer his first professional loss in the same year to unified heavyweight champion Wladimr Klitschko.
Chagaev won the WBA (Regular) heavyweight title by defeating Fres Oquendo in 2014. He made one successful defence before losing the title to Lucas Browne in 2016. However, after Browne failed a drug test, the WBA reinstated Chagaev as champion, but he was once again stripped of the title in July of that year after failing to pay sanctioning fees. On 28 July 2016, he announced his retirement from boxing due to ongoing eye injuries. Chagaev won gold at the 1997 World Amateur Boxing Championships heavyweight, defeating Felix Savon in the finals, but later he was stripped of the championship for having 2 professional bouts in the United States before the tournament. Chagaev is the only non-Cuban boxer to defeat Félix Savón twice, and the only one to do it at the world championships, which Savón have won consecutively. Savón suffered his first international defeat in more than a decade, when he met Chagaev for a first time. His amateur career is also merited with absence of stoppages on his part, with all four his losses were standing defeats with him being outpointed. Because of his performance at the 2001 World Amateur Boxing Championships, where Chagaev stopped every opponent he had faced – a rarity in amateur boxing competitions, – Chagaev received the nickname "White Tyson".
