The cable news network said it had terminated its top-rated anchor Chris Cuomo, a move that came four months after Andrew Cuomo resigned as governor of New York.

Iran PressAmerica: He was fired by CNN on Saturday, completing a stunning downfall for the network’s top-rated anchor amid an ongoing inquiry into his efforts to help his brother, Andrew M. Cuomo, then the governor of New York, stave off sexual harassment accusations.

Until last month, Mr. Cuomo had enjoyed the support of CNN’s president, Jeff Zucker, and he faced no discipline for his behind-the-scenes strategizing with Andrew Cuomo’s political aides, a breach of basic journalistic norms.

But the anchor was suspended on Tuesday after a new batch of testimony and text messages, released by the New York attorney general, revealed a more intimate and engaged role in his brother’s political affairs than the network said it had previously known. CNN said on Saturday that it had enlisted outside counsel to review Mr. Cuomo’s actions, a sign that its inquiry quickly entered a more serious stage.

“We retained a respected law firm to conduct the review, and have terminated him, effective immediately,” CNN said in a statement. “While in the process of that review, additional information has come to light. Despite the termination, we will investigate as appropriate.”

The network declined to elaborate on any new facts that had emerged.

As the gregarious and sometimes combative host of CNN’s 9 p.m. hour, Mr. Cuomo was at the peak of a broadcast journalism career that he had forged outside of his famed political family. But it was the troubles of his brother, who resigned the governorship in August, that ultimately embroiled Mr. Cuomo in a controversy that precipitated his dismissal.

“This is not how I want my time at CNN to end but I have already told you why and how I helped my brother,” Chris Cuomo said in a statement on Saturday. “So let me now say as disappointing as this is, I could not be more proud of the team at ‘Cuomo Prime Time’ and the work we did as CNN’s #1 show in the most competitive time slot.”

Documents released on Nov. 29 revealed that the anchor offered advice on Andrew Cuomo’s public statements and made efforts to uncover the status of pending articles at other news outlets, including The New Yorker and Politico, concerning harassment allegations against the governor.