Twitter co-founder Jack Dorsey is stepping down as CEO of the social media platform, the company has announced.
He will be succeeded by Twitter's current chief technology officer, Parag Agrawal.
Mr Dorsey will remain on the board until his term expires in 2022.
Mr Agrawal joined Twitter in 2011 and has been CTO since 2017.
In a letter posted on his Twitter account, Mr Dorsey said he was "really sad... yet really happy" about departing the company and that it was his decision.
He tweeted it was "finally time for me to leave".
On Sunday, Mr Dorsey had sent a tweet reading only "I love Twitter".
He has faced several distractions as CEO, starting with the fact that he's also founder and CEO of the payments company Square.
Some big investors have openly questioned whether he could effectively lead both companies.
Last year, the company came to an agreement with two of those activist investors that kept Mr Dorsey in the top job and gave a seat on the company board to Elliott Management Corp, which owned about four per cent of Twitter's stock, and another to Silver Lake.
Mr Dorsey took the controversial decision to permanently ban Donald Trump from the platform, where the former president had amassed 88.7 million followers.
Mr Dorsey made the decision days after Mr Trump whipped up a mob of supporters who stormed the US Capitol, where they tried to prevent Joe Biden being confirmed winner of the 2020 election.
Supporters of the former president accused Mr Dorsey and the social media giants of trying to curb free speech, and many quit to join new, far-right-friendly platforms.
But some also defended the hard decisions Mr Dorsey had to make.
"People tend to conflate jack dorsey with twitter censorship, but my sense is he's actually done what he could these past few years to keep the platform relatively open," tweeted Mike Solana, head of the private equity firm Founders Fund.
"Things will be worse without him, not better. godspeed, bird king." he added.
While Twitter has high-profile users like politicians and celebrities and is a favourite of journalists, its user base lags far behind old rivals like Facebook and YouTube and newer ones like TikTok.
It has about 200 million daily active users, a common industry metric.
The early days of Twitter began with a tweet sent by Dorsey on March 21, 2006, that read "just setting up my twttr".
Twitter went through a period of robust growth during its early years but as its expansion slowed the San Francisco company began tweaking its format in a bid to make it easier and more engaging to use.
Mr Dorsey became Twitter CEO in 2007 but was forced out the following year.
He returned to the role in 2015.
In his goodbye letter, Mr Dorsey said he has "worked hard to ensure this company can break away from its founding and founders", and that to focus too much on whether companies are led by their founders is "severely limiting".
Facebook COO Sheryl Sandberg, left, accompanied by Twitter CEO Jack Dorsey are sworn in before a Senate Intelligence Committee hearing. Source: AAP
Twitter also announced on Monday a new board chairman, Bret Taylor, to replace its existing chair Patrick Pichette.
Mr Pichette will remain on the board.
Mr Taylor has been on Twitter's board since 2016 and is the president and COO of business software company Salesforce.
