The account, which has the username @michelleobama, will be managed by President Barack Obama's 2012 campaign staff, but any postings written by the wife of the president will be signed "-mo."
Soon after the account was created, the president's Twitter account gave a shout out to the first lady.
"It's not every day we get to welcome the First Lady of the United States to Twitter -- happy to have you," read a posting from Obama's account, which is also managed by his 2012 campaign staff.
In her first tweet, the first lady wrote, "Hi, everyone, and thanks for the warm welcome. Look forward to staying in touch with you here. -mo."
"I love that you're on Twitter @michelleobama! Finally a forum to discuss the important topics with you. Have you been watching The Bachelor?" DeGeneres joked.