Twitter CFO Anthony Noto will replace Bain, who Twitter said is leaving to "explore opportunities outside the company."
The departure of Bain, who was once on the shortlist to be Twitter's CEO, leaves Twitter without one of the online ad industry's most respected execs at a time when the company is facing mounting pressure to increase its revenue.
And the move elevates Noto to the most powerful figure inside the company after Jack Dorsey, whose time is divided between CEO jobs leading Twitter and online payments company Square.
Noto will relinquish his duties overseeing Twitter's finances and will take over all of the company's revenue-generating products and business partnerships. Twitter is looking for a new CFO to replace Noto, the company said,
Shares of Twitter, which announced plans to cut hundreds of jobs last month, slid as much as 4% in after hours trading on Wednesday.
No compete and no severance
"After 6 years and a once-in-a-lifetime run, I let Jack know that I am ready to change gears and do something new outside the company," Bain said in a tweet.
Bain notified Twitter of his decision to leave on November 7, accoring to the company. And he has agreed not to work for competitors such as Facebook, the New York Times reported.
Bain will not get any severance compensation as he is leaving of his own accord, a Twitter spokesperson told Business Insider.
The executive shuffle is the latest chapter in Twitter's tumultuous history, which has included a string of CEO changes and seemingly constant infighting among the founders. And it consolidates the 48-year old Noto's power at the company.
A former Wall Street banker and ex-Army Ranger, Noto joined Twitter in 2014 and quickly caused ripples internally with a lavish, $73 million compensation package that was out of step with the company's past pay practices.
Noto has increasingly expanded his role beyond finance, spearheading the company's recent push into live video of sporting events like the deal with the NFL. But with Twitter's user growth stuck in the mud and speculation swirling that the company could be acquired, Noto will now have to prove he can revitalize the company. Or find someone to buy it.
Can't tell you how much I will miss U my friend. Couldn't imagine that last 3 yrs w/out U. U have had a tremendous impact on Twitter TY https://t.co/GqRUvNGhv6-; Anthony Noto (@anthonynoto) November 9, 2016
Bain was instrumental in building Twitter's advertising business, and his departure comes after the company shut down Vine and laid off 9% of its workforce last month in an effort to cut costs and work toward profitability in 2017.
"Since joining Twitter in 2010, Adam has built an amazing team and a global business from the ground up," Twitter CEO Jack Dorsey said in a statement. "I'm grateful to Adam for everything he's done for Twitter, and for his leadership and friendship over the years. I can't wait to see what he does next!"