McAllister, who largely self-funded his campaign, beat establishment candidate Neil Riser, a state senator, in Saturday's runoff election for the vacant 5th District seat.
Both men are Republicans.
McAllister ran as a political outsider, capitalizing on voter frustration with politicians and Congress. Riser, a funeral home owner, campaigned on his experience in the Legislature and with the support of tea party groups.
Their strongest disagreement was on President Barack Obama's signature health care law.
Both opposed the health overhaul, but Riser wanted only repeal. McAllister said repeal had no chance with Democrats leading the Senate, so he said Congress should work on improvements to the law.