Mr Musk tweeted the news a day after confirming he had found a new person to take on the role.
He said that Ms Yaccarino "will focus primarily on business operations, while I focus on product design and new technology".
accarino has worked at NBCUniversal for nearly 12 years - with her team generating more than $100 billion in ad sales since 2011, her company bio notes. According to LinkedIn, Yaccarino previously served as NBC's chair for advertising and client partnerships and as president of cable entertainment and digital advertising sales. Prior to her time with NBC, Yaccarino worked at global entertainment company Turner for almost two decades.
Yaccarino interviewed Musk on a Miami stage last month in front of hundreds of advertisers.
Luring advertisers is critical for Musk and Twitter after many fled in the early months after his takeover of the social media platform, fearing harm to their brands in the ensuing chaos. Musk said in late April that advertisers had returned, but provided no details.
Yaccarino could help restore advertisers' faith in Twitter, ad agency DiGo founder and creative chief Mark DiMassimo said. He noted that Yaccarino successfully integrated and digitized ad sales at Comcast and NBC - and that her track record of cross-selling ads across different platforms could appeal to Musk as he tries to transform Twitter from a social media company to a bigger media platform.
"If anyone can translate the Musk vision into advantages for marketers she'll be able to do it," DiMassimo said. "Even though there's skepticism and all marketers live in the `show me' state right now with regard to Twitter, if in fact she does go to Twitter this is a powerfully reassuring move."
Musk has long insisted he is not the company's permanent CEO. The Tesla billionaire said in a tweet Thursday that his role will transition to being Twitter's executive chairman and chief technology officer.
In mid-November, just a few weeks after buying the social media platform for $44 billion, he told a Delaware court that he does not want to be the CEO of any company.
More than a month later, he tweeted in December: "I will resign as CEO as soon as I find someone foolish enough to take the job." The pledge came after millions of Twitter users asked him to step down in a Twitter poll the billionaire himself created and promised to abide by.
In February, he told a conference he anticipated finding a CEO for San Francisco-based Twitter "probably toward the end of this year."
Analysts who follow Twitter's business welcomed the news even without knowing who the replacement will be. Twitter's advertising business has taken a hit under Musk's mercurial rule, though the billionaire told BBC last month that the company is now "roughly" breaking even.
"A new CEO is the only way forward for Twitter," said Insider Intelligence analyst Jasmine Enberg.
"The single biggest problem with Twitter's ad business was Elon Musk. As he steps back, Twitter can begin to unravel Musk's personal brand from the company's corporate image and attempt to regain trust among advertisers," Enberg said. "The success of those efforts will depend on who takes over, but it's difficult to imagine that the new CEO could be more controversial or damaging to Twitter's ad business than Musk has been."
Mike Proulx, research director at Forrester Research, added that advertising is not the only challenge that Twitter's new CEO will face - after all, Musk has "fundamentally altered" Twitter both as a product and a community, arguably "for the worst."
"While he's stepping back from the CEO title, Musk is far from likely to step back from calling the product shots," Proulx said.
Shares of Tesla rose about 2% Thursday after Musk made the announcement. Shareholders of the electric car company have been concerned about how much of his attention is being spent on Twitter.
Last November, Musk was questioned in court about how he splits his time among Tesla and his other companies, including SpaceX and Twitter. Musk had to testify in the trial in Delaware's Court of Chancery over a shareholder's challenge to his potentially $55 billion compensation plan as CEO of the electric car company.
Musk said he never intended to be CEO of Tesla, and that he didn't want to be chief executive of any other companies either, preferring to see himself as an engineer. Musk also said at the time that he expected an organizational restructuring of Twitter to be completed in the next week or so. It's been nearly six months since he said that.
Musk's tenure at Twitter's helm has been chaotic, and he's made various promises and proclamations he's backtracked or never followed up on. He began his first day firing the company's top executives, followed by roughly 80% of its staff. He's upended the platform's verification system and has scaled back content moderation and safeguards against the spread of misinformation.
Bantering with Twitter followers late last year, Musk expressed pessimism about the prospects for a new CEO, saying that person "must like pain a lot" to run a company that "has been in the fast lane to bankruptcy."
"No one wants the job who can actually keep Twitter alive. There is no successor," Musk tweeted at the time.