The daily tracking poll does not include any polling done after Tuesday night's debate, Gallup said. The numbers were based on a rolling seven-day average through Tuesday.
The poll gave Romney 51 percent of the vote to 45 percent for President Obama, Gallup said. Romney's lead diminished among registered voters to 48 percent to 46 percent.
Romney's lead is his largest so far from Gallup with the election just three weeks away, The Hill reported. But the Real Clear Politics average of all national polls gave Romney a much smaller lead, 47.6 to 47.
The tracking poll has a margin of error of 2 percentage points.