Gingrich now has 31% support from registered Republican voters in the Gallup daily tracking poll, compared with 27% for the former Massachusetts governor.
The former House speaker now has completely erased a 23-point advantage Romney enjoyed earlier this month. Gingrich's standing reflects a surge last week, when he pulled in two strong debate performances and soundly defeated Romney in the Jan. 21 South Carolina primary.
The poll, a five-day rolling average, reflects a change from yesterday, which showed Gingrich and Romney in a dead heat.
In hypothetical matchups taken in mid-December, President Obama would lead both Romney and Gingrich, 50%-48%.
Gallup's Frank Newport said in a blog post yesterday that Gingrich's gains have come mostly from conservative Republicans. Gingrich jumped by 12 percentage points with that voting group, as Romney's support among conservatives fell.
Rick Santorum and Ron Paul each have 12% support among GOP registered voters nationwide, Gallup says.