Mitch McConnell, the Republican majority leader, said Ms Warren had broken Senate rules by impugning the conduct of another senator.
She is now banned from speaking in the Senate until the end of Mr Sessions` nomination process. The vote is expected on Wednesday.
The incident has outraged Democrats, and delighted Ms Warren`s detractors.
So what is the rule that gagged her, and was it fairly applied?
How did this happen?
The incident occurred during a debate in the Senate on the nomination of Mr Sessions.
Elizabeth Warren started reading a 1986 letter by Coretta Scott King, written to oppose President Reagan`s nomination of Mr Sessions as a federal judge.
Ms Scott King`s letter alleged that Mr Sessions was unsuitable for that role because he had "used the awesome powers of his office in a shabby attempt to intimidate and frighten elderly black voters".
Ms Warren also quoted the late Senator Ted Kennedy, who called Mr Sessions a "throwback to a shameful era".
Mr Sessions` nomination process has been dogged by allegations of racism.
Mr Sessions has denies the allegations, and his supporters have pointed to his vote to extend the Voting Rights Act.
Ms Warren`s reading was interrupted by the Senate`s presiding officer, Republican Senator Steve Daines of Montana, who said she was breaking a rule that stops senators accusing each other of "unbecoming" conduct.
Mitch McConnell, the Republican majority leader, agreed.
His objection to Ms Warren`s speech was put to a vote, and the Senate voted to silence Ms Warren by 49 to 43.
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