Bitcoin evangelist Charles Shrem will plead guilty Thursday to one criminal count stemming from what prosecutors had alleged was a drug scheme involving his virtual-currency exchange and an online black market, according to court documents.

Mr. Shrem, a well-known bitcoin advocate, will enter the plea in federal court in Manhattan next week, he confirmed in an interview. He said he would plead to one count of aiding and abetting an unlicensed money transmission.

"I'm happy that it's coming to a close," said Mr. Shrem in the telephone interview.

Mr. Shrem and his alleged accomplice, Robert Faiella, had previously pleaded not guilty to running an alleged money-laundering scheme that funneled the digital currency to users of the online alleged black-market site Silk Road. Mr. Faiella's lawyer didn't respond to requests for comment.

Mr. Shrem was arrested in January along with Mr. Faiella in what the Manhattan U.S. attorney's office said was a conspiracy to help Silk Road customers anonymously purchase illegal items, including narcotics and forged passports, online. They were charged in an indictment with conspiracy to commit money laundering and operating an unlicensed money-transmitting business.