The ECB's move to protract monetary stimulus came amid jitters about slowing growth in the euro zone, political turmoil in Italy and global trade tension, analysts said.
"We didn't discuss when to raise rates," ECB President Mario Draghi said at a press conference following the central bank's policy meeting.
This stance contrasts with the steady rate-hike campaign that the Federal Reserve signaled on Wednesday. The ECB's willingness to preserve easy money to help its economy soured bullish bets on the single currency and caused traders to pile into the dollar and yen.
"The market was caught wrong-footed as the rates would be on hold into mid-2019," said Peter Ng, senior currency trader at Silicon Valley Bank at Santa Clara, California.
The dollar against a basket of major currencies traded up 1.14 percent at 94.78, its highest level May 29, when it hit 94.83.
Against the Japanese yen, the dollar strengthened 1.69 percent to 1.159.
Meanwhile, the euro shed 1.68 percent at $1.1591 after briefly posting its steepest daily drop against the dollar in nearly two years.
Investors now price just a 30 percent chance of a 10 basis point rate hike by July 2019, compared with a roughly 80 percent chance earlier in the day. On the other hand, the U.S. central bank is expected to raise short-term interest rates twice more in 2018 and likely to lift them three times in 2019, according to a Reuters poll.
On Wednesday, the Fed, as expected, raised short-term rates.
"There's obviously a divergence where rates are heading," Ng said. "This makes the dollar a lot more attractive to global investors."