Verizon shares are down 15 per cent this year.
The acquisition marks the end of the line for Yahoo as a standalone company, a storied Web pioneer once valued at more than US$100b.
Verizon is rebranding AOL and Yahoo as part of a new venture called Oath, led by AOL chief executive Tim Armstrong.
Verizon is betting it can use data from more than 200 million unique monthly visitors to Yahoo sites and combine it with data on 150 million unique monthly AOL users and its own user base of more than 100 million wireless subscribers to offer more targeted services for advertisers.
The Yahoo deal came after activist investors led by Starboard Value LP lost faith in Yahoo CEO Marissa Mayer, who was hired in 2012, and forced the sale of the company's core assets. Mayer is not expected to remain at Yahoo after the sale is completed.
Yahoo is still one of the largest properties on the internet, with hundreds of millions of customers using its email, finance and sports offerings, and a heavily trafficked home page. In February 2016, Yahoo announced it was cutting 1,600 employees, or 15 per cent of its staff.
The deal's closing was delayed as the companies assessed the fallout from two Yahoo data breaches.
Yahoo disclosed in December that data from more than one billion user accounts was compromised in August 2013, making it the largest breach in history. This followed a separate disclosure that at least 500 million accounts were affected in a 2014 breach.