It was created by British start-up Exscientia and Japanese pharmaceutical firm Sumitomo Dainippon Pharma.
The drug will be used to treat patients who have obsessive-compulsive disorder (OCD).
Typically, drug development takes about five years to get to trial, but the AI drug took just 12 months.
Exscienta chief executive Prof Andrew Hopkins described it as a “key milestone in drug discovery”.
He told the BBC: “We have seen AI for diagnosing patients and for analysing patient data and scans, but this is a direct use of AI in the creation of a new medicine.”
The molecule – known as DSP-1181 – was created by using algorithms that sifted through potential compounds, checking them against a huge database of parameters.
“There are billions of decisions needed to find the right molecules and it is a huge decision to precisely engineer a drug,” said Prof Hopkins.
“But the beauty of the algorithm is that they are agnostic, so can be applied to any disease,” he added.
The first drug will enter phase one trials in Japan which, if successful, will be followed by more global tests.
The firm is already working on potential drugs for the treatment of cancer and cardiovascular disease and hopes to have another molecule ready for clinical trials by the end of the year.
“This year was the first to have an AI-designed drug but by the end of the decade all new drugs could potentially be created by AI,” said Prof Hopkins.
Paul Workman, chief executive of The Institute of Cancer Research, who was not involved in the research, said of the breakthrough: “I think AI has huge potential to enhance and accelerate drug discovery.
“I’m excited to see what I believe is the first example of a new drug now entering human clinical trials, that was created by scientists using AI in a major way to guide and speed up discovery.”