In a resignation letter posted on X, Mrinank Sharma informed the company that he was leaving because of his concerns about AI, bioweapons and the state of the world.
Sharma explained that he will now pursue writing and studying poetry and return to the UK to "become invisible".
The researcher led a team at Anthropic that researched AI safeguards and explained how contributions included investigating why generative AI systems suck up to users, combating AI-assisted bioterrorism risks and researching "how AI assistants could make us less human".
Despite enjoying his time at the company, Sharma explained that it was evident that "the time has come to move on".
He wrote: "The world is in peril. And not just from AI, or bioweapons, but from a whole series of interconnected crises unfolding in this very moment."
Sharma said how he had "repeatedly seen how hard it is to truly let our values govern our actions" and lamented how Anthropic employees "constantly face pressures to set aside what matters most".
The researcher explained how he plans to pursue a poetry degree and writing.
He added in a reply: "I'll be moving back to the UK and letting myself become invisible for a period of time."
Anthropic recently poked fun at rival OpenAI's decision to deploy adverts in the ChatGPT chatbot - despite pledges not to do so - and former OpenAI researcher Zoe Hitzig expressed that she was "really nervous about working in the industry".
She explained that her concerns stemmed from the potential psychological impacts of a "new type of social interaction" that is not yet fully understood.
Hitzig said that "early warning signs" that dependence on AI tools were "worrisome" and could "reinforce certain kinds of delusions".
She told the BBC's Newsnight programme: "Creating an economic engine that profits from encouraging these kinds of new relationships before we understand them is really dangerous.
"We saw what happened with social media."
Hitzig added: "There's still time to set up the social institutions, the forms of regulation that can actually govern this."
In response, an OpenAI spokesperson said: "Our mission is to ensure AI benefits all of humanity; our pursuit of advertising is always in support of that mission and making AI more accessible."
