The former House speaker has the support of 25% of likely Republican caucusgoers in the survey, up from just 7% in the previous one conducted in late October.
The state of play in Iowa has proven to be just as volatile as national surveys have indicated. Herman Cain, who announced Saturday that he was suspending his campaign, led Romney 23%-22% in that October survey.
Meanwhile, some of the candidates working hardest for a strong showing in the leadoff caucus state are in the back of the pack. Rep. Michele Bachmann of Minnesota has 8% support, equaling Cain. Rick Santorum and Rick Perry were tied at 6%.
According to the Register, Cain's support evaporated as the poll was in the field, starting at 12% and dropping to just 4% in the final day, after an Atlanta woman went public with claims that the two had engaged in a 13-year extramarital affair. Cain has denied the charge, saying he only provided financial support to the woman as a friend.
Gingrich, left for dead this summer after a bungling start to the campaign, has emerged as the GOP race's newest front-runner. And the Register says his support in Iowa could continue to grow -- 18% ranked him as their second choice.
Sixty percent of those surveyed said they still could change their mind. There are at least two debates scheduled, starting next weekend.
The Register's poll, conducted by the Des Moines-based Selzer & Company, is considered the most reliable poll of voters in the leadoff caucus state. This survey was conducted Nov. 27-30 from a sample of 401 likely Republican caucus-goers, and had a margin of error of 4.9%.
Iowa's Jan. 3 caucuses are the first nominating contest of the 2012 campaign.