Former cryptocurrency executive Sam Bankman-Fried is accused of stealing billions of dollars from his customers and investors over several years in the US in a trial that began on October 3.
News of the 31-year-old's testimony comes a day before the defence is set to cross-examine former executives of the company.
Bankman-Fried's lawyer Mark Cohen told Judge Lewis A Kaplan that he planned to call three witnesses "and then our client is also going to be testifying" after prosecutors rested early on Thursday.
Mr Cohen made the comment during a phone and video conference in Manhattan federal court after the judge told him: "It's time to tell me what defence case, if any, you're going to put on."
The judge told him that he did not have to say yet whether Bankman-Fried would testify, but Mr Cohen volunteered that he would.
Even so, prosecutors and the judge later discussed the possibility that closing arguments could occur early next week if Bankman-Fried changes his mind and does not take the stand.
Last week Bankman-Fried's lawyers argued that he needed a higher dose of ADHD medication to focus on the case and to “meaningfully” testify.
His lawyers said the one dose of Adderall their client is being given at jail early each morning, to treat his attention deficit hyperactivity disorder, wears off by the time the trial day starts.
The Massachusetts Institute of Technology graduate has pleaded not guilty in the case.
At trial, his lawyers have argued that he never intended to defraud anyone, and that many functions at the fledgling crypto exchange - including risk management - were "works in progress."
The former billionaire has already taken an unusual approach for a criminal defendant. Instead of laying low after he was charged, he published blog posts on his view of what went wrong and met with several journalists.
"I didn't steal funds, and I certainly didn't stash billions away," he wrote in January, a month after his arrest on US fraud charges.
Bankman-Fried denies charges that he looted the financial accounts of his customers and investors to live lavishly and bolster his personal reputation and the reputation of his companies through large donations to charity and political candidates.
Prosecutors have called some of his former top executives to testify against him.
They have told the jury that he was involved in every facet of his businesses and was fully aware that billions of dollars he was spending on real estate, investments and contributions were unwittingly funded by customers and investors.
Bankman-Fried has been jailed since August, when Judge Kaplan ruled that he had tried to influence potential trial witnesses and revoked the 250 million US dollar (£205 million) personal recognisance bond that had permitted him to live with his parents in Palo Alto, California, after his December extradition from the Bahamas.