Mattis and Kelly were confirmed by wide margins following the inauguration of President Donald Trump.
But objections from three Democratic senators delayed the vote on Pompeo until Monday, when the Senate set aside six hours to debate the nomination before voting.
"No CIA Director in history has ever been confirmed on Inauguration Day," Democratic Senators Ron Wyden, Patrick Leahy and Richard Blumenthal said in a joint statement.
The statement said a delay was needed because the position of CIA director requires a thorough vetting and debate.
Republicans argued that in times of increasing global threats against the United States, the Senate had an obligation to immediately confirm Trump’s senior national security team.
The nomination of Pompeo, a fourth term congressmen from the US state of Kansas, has generated controversy because of tensions between Trump and former CIA Director John Brennan.
The feud escalated when Trump accused intelligence officials of leaking the contents of a dossier prepared by Democrat-hired opposition researcher, which reportedly claimed Trump was vulnerable to blackmail because of compromising behavior during an earlier visit to Moscow.
Prior to his departure from the CIA at noon on Friday — when Trump was sworn as the 45th US president — Brennan had publicly accused Trump of lacking an understanding of Russia’s international capabilities, actions and intensions.
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