The former House speaker is on a two-campaign visit to Iowa, which will open the voting in the 2012 GOP contest next month and where anti-immigrant sentiment is intense.
"We haven't been able to build a fence on the border because we have not been a serious country," said Gingrich, as he prepared to sign the pledge following a morning speech to employees at Nationwide Insurance in Des Moines.
Gingrich, who has jumped to the top of the polls here and nationally, said his decision to sign the pledge was in line with his determination to offer "serious leadership doing serious things" as president.
He becomes the second GOP presidential candidate, after Rep. Michele Bachmann of Minnesota, to sign the pledge, which is being promoted by a North Carolina group, Americans for Securing the Border.
"For too long, too many politicians have given only lip service to the war on our border," said Van D. Hipp Jr., a former South Carolina Republican Party chairman and Washington defense consultant, who heads the group. He said he did not have a cost estimate for the fence.
The pledge contains a significant loophole: It leaves it up to the U.S. Border Patrol or Department of Homeland Security to determine locations for the fence.