Dmitri Kovtun will provide testimony by video-link after he was granted “core participant status” by the hearing’s chairman, Robert Owen.
Kovtun and Andrei Lugovoi are suspected of murdering the 43-year-old, who died nearly three weeks after consuming tea laced with polonium-210 in London in November 2006.
The pair deny any involvement and remain in Russia, having initially refused to take part in the inquiry, which is sitting at the Royal Courts of Justice in London.
However, in March Kovtun dramatically changed his mind and offered to give evidence.
Owen said he would grant him core participation status and allow him to give evidence if he meets a number of conditions.
A statement issued by the inquiry last night confirmed: “
Sir Robert is satisfied that Mr Kovtun has complied in full with his directions dated April 2, 2015.
“In complying with the directions Mr Kovtun has said that he is willing to: 1) attend a video-link evidence session in Moscow on dates specified by the chairman; 2) co-operate with the inquiry regarding arrangements for that evidence; and 3) that he does intend to assert the privilege against self-incrimination.”