Both Christie and Fiorina stated their decision on Facebook, a day after the New Hampshire primary where they fared poorly in the poll won by Donald Trump by a huge margin while Ohio Governor John Kasich finished a distant second.
In a Facebook post, Christie said that the government needs to once again work for the people, not the people working for the government.
"I have both won elections that I was supposed to lose and I've lost elections I was supposed to win and what that means is you never know what will happen. That is both the magic and the mystery of politics - you never quite know when which is going to happen, even when you think you do. And so today I leave the race without an ounce of regret," Christie said.
"Our Republican Party must fight alongside these Americans as well. We must end crony capitalism by fighting the policies that allow it to flourish," said the former Hewlett-Packard CEO.
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"We must fix our festering problems by holding our bloated, inept government bureaucracy accountable. Republicans must stand for conservative principles that lift people up and recognise all Americans have the right to fulfil their God-given potential," Fiorina said.
Apart from Trump and Kasich, the other candidates still in the race are Senators Ted Cruz and Marco Rubio, former Florida Governor Jeb Bush, and eminent neurosurgeon Ben Carson.
All these candidates are now campaigning in South Carolina where the next Republican primary is scheduled to be held later this month.