Fox Business Network, host of the debate, announced Monday that neither former Hewlett Packard CEO Fiorina nor Paul, a Kentucky senator, qualified based on Fox's criteria. Paul's campaign has vowed to boycott the event.
To qualify, candidates had to be in the top six of an average of recent national polls recognized by the network, or be in the top five of an average of the most recent polls in Iowa and New Hampshire, the first two primary states. Fox said it utilized 17 separate polls to reach its main stage lineup.
Those who qualified for the main stage are Donald Trump, Texas Sen. Ted Cruz, Florida Sen. Marco Rubio, Dr. Ben Carson, New Jersey Gov. Chris Christie, former Florida Gov. Jeb Bush, and Ohio Gov. John Kasich.
Though highly touted as his political career began, Paul's presidential campaign has struggled to raise money or draw interest to his Libertarian views, which include a non-interventionist foreign policy that puts him closer to Sen. Bernie Sanders of Vermont than any of his GOP rivals.
Paul said he would follow through on his promise to avoid the event, to be held in North Charleston, S.C., if he wasn't included on the main stage and would instead campaign in New Hampshire and Iowa.
He argued polls haven't shown his campaign's recent momentum and that if you exclude the margin of error, he is well above the Fox cutoff.
"I think if you have a national campaign, you've raised a significant amount of money, you're on the ballot, you've employed staff and you're actively campaigning, you've got to be in the debate," Paul said last week.
Fiorina briefly shot up in the polls after a standout performance in an undercard debate last fall, but has since fallen back to low single digits.