The social media company said on Tuesday it was taking action against online behaviour "that has the potential to lead to offline harm".
The decision comes after the events last week in Washington DC, where a mob of pro-Trump loyalists tried to violently storm the Capitol building.
"Since Friday, more than 70,000 accounts have been suspended as a result of our efforts, with many instances of a single individual operating numerous accounts", Twitter said in a blog post.
"These accounts were engaged in sharing harmful QAnon-associated content at scale and were primarily dedicated to the propagation of this conspiracy theory across the service", Twitter said.
Twitter chose to permanently suspend President Donald Trump's account after years in which Trump tested the boundaries of what he could say, violating the company's rules against election misinformation, glorifying violence, and falsehoods about COVID-19. The far-right QAnon conspiracy theory claims Trump is waging a secret war against a global liberal cult of Satan-worshipping pedophiles.
Twitter has previously tried to crack down on QAnon, and removed more than 7,000 accounts in July. But conservatives and the president's allies are accusing Twitter and other social media companies of censorship.
The social network began its purge on Friday, shortly after it had permanently suspended Trump's account for language that could incite violence. "We will not be SILENCED!" The company alleged that Parler had violated the terms of service of its cloud computing division, Amazon Web Services (AWS), for failing to deal with an increase in violent social media.
Facebook and Twitter have both indefinitely suspended the accounts for Trump, who has refused to accept the result of the November 3 election and spread baseless theories that the vote was rigged.
There was a protest outside of Twitter's headquarters in San Francisco, but it was lightly attended.