The equestrian athlete won a silver medal at the 2008 Olympics in Beijing. London is his fourth Olympic games.
Bengtsson also won the European championships in show jumping last autumn, and was recently awarded Swedish Sport Radio's prestigious sports personality of the year prize, Jerringpriset.
"He's a fantastic role model, he's been ranked number one in the world. It was an easy choice", said Stefan Lindberg, chairman of the Swedish Olympic Committee.
Other flag bearers at the ceremony will be Jamaica's Usain Bolt and Russia's Maria Sharapova.