Businessman Vance McAllister (R) won a Louisiana special election runoff for U.S. House Saturday, upsetting state Sen. Neil Riser (R) by nearly 20 points.

With all precincts reporting, McAllister claimed nearly 60 percent of the vote, according to the Associated Press's tally. McAllister will become the representative of Louisiana's 5th district, a sprawling area in the northeastern part of the state bounded by Arkansas to the north and Mississippi to the east.

No candidate claimed a majority of the vote in the open primary, triggering Saturday's runoff. But Riser was the top vote-getter in the primary, taking 32 percent of the vote to McAllister's 18 percent. Riser also had the support of House Majority Leader Eric Cantor (R-Va.).

McAllister has never held public office before. He relied mostly on self-funding, giving his campaign at least $235,000 and loaning it another $170,000, campaign finance records show. McAllister was also backed by "Duck Dynasty" star Willie Robertson, who cut an ad for him late in the race.

"A self-made businessman and Louisiana native, Vance’s priorities of fiscal responsibility and accountability will be an excellent addition to Louisiana’s delegation here in the Washington," said National Republican Congressional Committee Chairman Greg Walden in a statement.

McAllister will succeed Republican Rodney Alexander, who stepped down earlier this year for a post in the administration of Gov. Bobby Jindal (R).