Bond purchases are now running at a maximum of €30 billion (R470 billion) per month, but will be lowered to €15 billion (R235 billion) per month from September, before being completely stopped at the end of December.
The move is a major step towards dismantling the policies brought in to stabilise the eurozone in the wake of the financial crisis.
The ECB's statement reflected the battle between hawks and doves on the bank's council, with the decision on QE matched by a softening of its approach to interest rates.
"The Governing Council anticipates that, after September 2018, subject to incoming data confirming the Governing Council's medium-term inflation outlook, the monthly pace of the net asset purchases will be reduced to €15 billion until the end of December 2018 and that net purchases will then end", the European Central Bank said in a statement.
After that, it expects to reduce purchases to €15bn a month until the end of December 2018, when "net purchases will then end".
The ECB began its asset purchase programme in 2015, years after the United Kingdom and U.S. took similar action to shore up their economies.
It has so far pumped more than two trillion euros into the bloc's economy, while keeping interest rates at or near zero.
The central bank will debate whether to end its huge asset purchases by year-end, which was a crisis-era stimulus credited with pulling the euro zone economy out of recession.
The euro lost more than a cent against the dollar after the news, with dealers contrasting the decision to leave rates unchanged in the eurozone for at least a year, with signs from the Federal Reserve that it planned two further increases in U.S. rates in 2018 and three more in 2019.