The plan calls for the ECB to buy short-term bonds with no set limit, "to address severe distortions in government bond markets which originate from, in particular, unfounded fears on the part of investors of the reversibility of the euro."
Draghi said, "the euro is irreversible." He also said for the bank to buy a government's bonds that government would have to commit to fiscal goals that would comply with standards set up by the international rescue facilities.
The bonds would be purchased "under appropriate conditions," he said.
"Governments must stand ready to activate the European Financial Stability Facility - European Stability Mechanism in the bond market when exceptional financial market circumstances and risks to financial stability exist," he said.
Bond buying would be contingent on "strict and effective conditionality in line with established guidelines," Draghi added.
The announcement appears to answer to Draghi's statement over a month earlier in which he said the ECB would do "whatever it takes to preserve the euro."
That statement was followed up with an ECB policy meeting that came and went with no bond-buying program announced, disappointing investors.
Draghi did say earlier that governments would first need to request international help before the ECB would act.
The German Central Bank had opposed a bond-buying initiative. Germany has also been the principal player in Europe's insistence that help be granted only with pledges of renewed fiscal discipline.
Tying the bond-buying program to fiscal discipline could appease Germany to some degree.