After a short lived professional basketball career in Iceland, Björnsson injured his knee forcing an early retirement from the sport, he then in 2008 met Magnús Ver Magnússon, a 4 time World's Strongest Man winner who said Hafþór seemed a good prospect for a strongman. In 2010 he came 3rd in Iceland's Strongest Man, and has won every year since then. He has also won Europe's Strongest Man in 2014 and has appeared in 4 World's Strongest Man finals through 2011-2014, finishing in 6th, 3rd, 3rd, and 2nd respectively. Only narrowly missing the title in 2014 to Lithuanian 4x World's Strongest Man winner, and friend of Hafþór's, Žydrūnas Savickas. Savickas was the previous reigning champion as Europe's Strongest Man since 2010, but did not compete in 2014 (Savickas won in 2010, 2012, and 2013, but the Europe's Strongest Man competition was on hiatus in 2011 and no champion was named that year).