Purchases of mainly government bonds - at 60 billion euros a month - are now seen running until at least March 2017 instead of next September.
He also said that proceeds from the various assets bought would be reinvested back into the scheme.
"We decided to extend the asset-purchase program. The monthly purchases of 60 billion euros (£43.2 billion) under the asset-purchase program are now intended to run until the end of March 2017 or beyond if necessary and in any case until the Governing Council sees a sustained adjustment in the path of inflation consistent with its aim of achieving inflation below but close to 2 percent over the medium term," Draghi said.
Analysts polled by Reuters last week had expected the ECB to increase the monthly purchases to 75 billion euros as well as extending the purchases.
The purchases have pushed down yields and boosted lending, indicating that quantitative easing (QE) was working, even if only slowly and with a lag, supporting calls for more asset buys.
But critics have said QE has done little for inflation so far, the ECB's biggest worry, with headline figures hovering near zero and core inflation around 1 percent, well short of the central bank's target of nearly 2 percent
(Reporting by Balazs Koranyi Editing by Jeremy Gaunt.)
