Reports suggest he received a verified account with Twitter under the name @ConanOBrien and posted his first tweet from his dining room.
He has already acquired over 180,000 followers compared to Jay Leno's 30,000 followers.
O'Brien's tweet read: "Today I interviewed a squirrel in my backyard and then threw to commercial. Somebody help me".
O'Brien quit The Tonight Show in January 2010 and his exit deal with NBC reportedly prevents him from live interviews and TV appearances until September 2010.
He moved from New York to Los Angeles to take over The Tonight Show from Leno.