Obama, along with first lady Michelle Obama, walked into Oslo City Hall at 1 p.m. to a trumpet fanfare and sustained applause.
"I receive this honor with deep gratitude and great humility," he said. "It is an award that speaks to our highest aspirations - that for all the cruelty and hardship of our world, we are not mere prisoners of fate. Our actions matter, and can bend history in the direction of justice.
"And yet I would be remiss if I did not acknowledge the considerable controversy that your generous decision has generated. In part, this is because I am at the beginning, and not the end, of my labors on the world stage."