"The combined monthly purchases of public and private sector securities will amount to 60 billion euros" Draghi told assembled journalists at a press conference in Frankfurt.
The bond-buying programme will continue "until we see a sustained adjustment in the path of inflation which is consistent with our aim of achieving inflation rates below, but close to, 2%", he added.
Spending €60 billion a month for that long would mean the bank injecting over €1.1 trillion into the economy.
The Euro immediately dropped sharply against the US dollar on the news.
The Financial Times reported that interest on German 10-year government bonds fell by two basis points (=0.1 percent) to 0.5 percent as investors scrambled to buy.
Meanwhile, interest on Greek debt fell 10 points to 8.9 percent, Spanish debt 7 points to 1.46 percent, and French debt four points to 0.66 percent.