Mr Derby-Lewis's Australian- born wife, Gaye, and a Polish immigrant, Janusz Walus, had been charged earlier with the killing.
Police said yesterday that Mr Derby-Lewis, 57, a former Conservative Party MP and a member of the advisory President's Council, would appear in court on Wednesday.
Mr Hani, who was shot dead outside his home near Johannesburg on 10 April, was the former leader of the armed wing of the African National Congress and a member of the ANC negotiating team at multi-party talks about the transition to non-racial democracy.
His assassination led to a series of bloody clashes between South African police and black protesters.
Mr Walus was arrested minutes after Mr Hani was killed. Officials say he was a member of the militant right-wing Afrikaner Resistance Movement and other groups opposed to apartheid reform.
Police have said they suspect Mr Hani's murder was part of a right-wing conspiracy. Clive Derby-Lewis was detained without charge under security laws on 17 April.
Antonie Gildenhuys, head of a multi-party peace committee, yesterday praised the investigation into Mr Hani's murder. He said three European police observers monitoring the investigation had told him that the South African police work was thorough.Reuse content