The period drama, which was written by Julian Fellowes, focuses on the Crawley family and the servants working for them.
The third episode aired on Sunday night, picking up overnight ratings of 8.1m.
ITV has now revealed that it has recommissioned the series, which stars Dame Maggie Smith, Hugh Bonneville, Brendan Coyle, Penelope Wilton and Elizabeth McGovern.
ITV's director of drama commissioning Laura Mackie said: "We're delighted with the audience response to Downton Abbey and the positive critical reaction. We're extremely proud to have commissioned a series which has clearly captivated ITV1 viewers.
"Consequently, we're thrilled to be announcing the recommission of a new series for 2011 which will allow us to spend more time with the Crawley family and their servants."
The current series of Downton Abbey continues on Sunday at 9pm on ITV1.