The US President began the session on Wednesday afternoon, with the rush of traffic crashing the site's servers within the hour.
Obama confirmed the AMA on his Twitter account, and began the chat with a verification photo and the message: "Hey everybody - this is barack. Just finished a great rally in Charlottesville, and am looking forward to your questions."
By 5pm, the thread had received nearly 10,000 comments from Reddit users.
The President, who is battling Republican nominee Mitt Romney for re-election in November, was asked a variety of questions on topics such as the space programme, his plans should he win the election, and basketball, before the site became unavailable for many users.
When asked by a commenter whether internet freedom would form part of the Democratic Party platform in 2012, Obama responded: "Internet freedom is something I know you all care passionately about; I do too.
"We will fight hard to make sure that the internet remains the open forum for everybody - from those who are expressing an idea to those to want to start a business.
"And although there will be occasional disagreements on the details of various legislative proposals, I won't stray from that principle - and it will be reflected in the platform."