His breakthrough season came in 2003, where he won his first gold medal in the Middle Distance. Gueorgiou has since won all 3 individual disciplines, winning the Sprint Distance for the first time in Kyiv in 2007 and the Long Distance for the first time in 2011. Gueorgiou won his most recent Long Distance gold medal in 2015, winning the gold in the Long Distance at Glen Affric ahead of Daniel Hubmann and Olav Lundanes. Thierry has won 14 gold medals at world championships.