Musk, who runs Tesla and Space X, said a day prior that he plans to transition to a role as executive chairman and chief technology officer.
Yaccarino "will focus primarily on business operations, while I focus on product design & new technology," Musk said on Friday. "Looking forward to working with Linda to transform this platform into X, the everything app," he added.
The announcement comes months after Musk pledged in December to step down as the head of Twitter as soon as he found someone "foolish enough to take the job."
Yaccarino, who stepped down earlier on Friday as the ad sales chief at NBCUniversal, oversaw an international team of about 2,000 employees, according to the NBCUniversal website.
She brings longstanding relationships with major advertisers and a strong reputation within the corporate community, experts told ABC News.
"She transformed advertising at NBCUniversal," Mike Proulx, a vice president and research director at Forrester, told ABC News. "If she succeeds, Twitter succeeds."
Yaccarino worked at NBCUniversal for nearly 12 years, rising through the executive ranks to become chairman of global advertising and partnerships in 2020.
Before NBCUniversal, Yaccarino served as an advertising executive at Turner Broadcasting Company for almost 20 years.
After acquiring Twitter in October, Musk has sought to shore up the company's finances by slashing costs and expanding revenue through a revamped version of its subscription service.
The hiring of Yaccarino, however, suggests a renewed focus on advertising, which accounts for the vast majority of Twitter's revenue, Dan Ives, a managing director of equity research at Wedbush, an investment firm, told ABC News.
"The heart and lungs of Twitter's monetization is advertising and Musk realizes that's not going to change," Ives said. "He needs an advertising guru front and center leading the charge of Twitter."
Who is Linda Yaccarino?
Yaccarino, who graduated from Penn State University in 1985, worked in media advertising for about 30 years before being named Twitter CEO on Friday.
Over more than a decade at NBCUniversal, Yaccarino generated more than $100 billion in advertising sales, focusing recently on an effort to coordinate advertising across TV, streaming and online platforms, the company's website said in a profile of Yaccarino that was removed on Friday.
When NBC launched its streaming service Peacock in 2020, for instance, Yaccarino led a campaign to offer an array of ad formats, such as binge ads that afterward allow a viewer to watch ad-free as well as ads that include a QR-code directing viewers to a product.
"It helped close the loop between television advertising and mobile use," Proulx said. "Her background is clearly based in big-brand advertising."
Ives, of Wedbush, echoed the sentiment: "She has a strong advertising DNA from NBCUniversal."
Beyond the workplace, Yaccarino holds an active role with the World Economic Forum, the organization that hosts the annual meetup of business and political leaders in Davos, Switzerland. She leads the task force on the future of work and holds a seat on the media, entertainment and culture industry governors steering committee.
Yaccarino drew attention in 2018 when then-President Donald Trump appointed her to the President's Council on Sports, Fitness and Nutrition.
How could Linda Yaccarino change Twitter?
In her new role, Yaccarino will wield significant weight as she likely aims to reestablish marketing relationships between Twitter and major brands after many reduced their presence on the platform or exited entirely due to concerns over changes implemented by Musk, experts said.
Musk, who frequently reiterates his commitment to protecting free speech, will likely disagree with Yaccarino over the extent to which the platform should moderate content as a means of attracting and retaining major brands, they added, potentially complicating her plans, experts said.
"There has been considerable damage done in the realm of trust for the advertising community on Twitter," Proulx said. "This will rely not just on her credibility with the advertising community but actually demonstrating that Twitter is prioritizing brand safety."
"That's the ultimate question," he added.
On its last quarterly earnings report before going private, Twitter said last July that advertising accounted for some 91% of overall revenue.
Since he took over, Musk has sought to rejuvenate the platform's subscription offering, Twitter Blue, as a means of reducing its dependence on advertising revenue. Meanwhile, many of Twitter's top advertisers, like Coca-Cola and Unilever, stopped spending money on the platform.
In an effort to significantly slash costs, the company has cut roughly 75% of its 7,500-person workforce, raising concerns about Twitter's capacity to maintain its platform.
Musk has defended his actions at Twitter as part of an aggressive effort to rescue the company from financial peril, which he described in a Twitter Spaces interview in December as an "emergency fire drill."
However, the strategy shift has made little improvement in revenue generated by the subscriptions, while the loss of ad dollars has threatened the core business, Proulx said.
"The hope was that Twitter Blue would offset the heavy reliance on advertisers, but that just has not even remotely come close to fruition," Proulx said.
Yaccarino will push the company to strike a balance between permitting a wide range of content on the platform and making the site palatable for major advertisers, Ives said.
"The Musk antics and controversy are what advertisers don't want," he said. "It will eventually come to a head."
Because Musk owns the company and plans to retain a key leadership role, Yaccarino will face a challenge exerting control over the company, experts said, noting that her stature within the industry will afford her greater leverage with Musk.
"She'll have quiet autonomy," Peter Harms, a professor of management at the University of Alabama, told ABC News. "I suspect Musk will continue making proclamations and suggesting directions and product features. But ultimately the day-to-day working is going to be in her hands."
Echoing that sentiment, Proulx said: "There are very few individuals that can assume that role with the level of gravitas that is needed to stand on their own outside of the halo of Elon Musk and she is one of those people."
New Twitter CEO will be Linda Yaccarino, Elon Musk says originally appeared on abcnews.go.com