Mann was moved from a jail in Harare to Equatorial Guinea in February
Prosecutors in Equatorial Guinea have called for British mercenary Simon Mann to serve 30 years in jail for his 2004 coup plot, as his trial got under way.
They have also named Sir Mark Thatcher, son of former UK Prime Minister Margaret Thatcher, as a plot organiser.
Mr Mann admitted his own involvement in March, although he said he was not the "main man" behind the plot.
Sir Mark was fined in 2005 and received a suspended sentence in South Africa for unknowingly helping to finance it.
Mr Mann, an ex-SAS officer, was arrested four years ago with 64 others in Zimbabwe.
He served four years in prison there for trying to purchase weapons without a licence before being extradited to Equatorial Guinea earlier this year.
Public prosecutor Jose Olo Obono has said the charges against Mr Mann merited the death penalty, but that waiving the death sentence had been a precondition of Mr Mann's extradition.
The trial is being held at a conference centre in the capital, Malabo, and began amid heavy security.
Mr Mann arrived at the courtroom wearing a grey prison outfit with blue stripes on the back, AFP news agency reported.
Journalists were allowed into the courtroom but made to leave mobile phones, cameras and even pens and notepads outside. News reports said that a verdict was expected by Thursday.
Eleven other men, including South African arms dealer Nick Du Toit who testified that he was recruited by Mr Mann, are already serving sentences in Equatorial Guinea in connection with the coup attempt.
Du Toit also said he had been told they were trying to install an exiled opposition politician, Severo Moto, as president. Mr Moto has been sentenced to a long prison term in absentia for his role.
Last week, Mr Olo Obono said Mr Mann would face three charges - crimes against the head of state, crimes against the government and crimes against the peace and independence of the state.
President Teodoro Obiang Nguema told Channel 4 News: "We've reached a conclusion that Simon Mann was used as an instrument, but there were material and intellectual authors behind it that financed the operation."
President Obiang has accused the Spanish government, a former British cabinet minister whom he refuses to name, oil tycoon Eli Calil and Mr Moto, who lives in Spain, of involvement. Both named men have strongly denied any links to the plot.
Mr Mann's lawyer, Jose Pablo Nvo, said he was working for his client "first, to not have a death sentence, and then to stay the least time possible in prison".
Mr Mann, a 55-year-old ex-Etonian who has been held in Malabo's notorious Black Beach prison since being extradited in February, told Channel 4 News a month later that he had been the "manager, not the architect" of the plot to overthrow Mr Obiang.
Mr Mann went on to name those who were "part of the team", including Sir Mark Thatcher.
Sir Mark was fined and received a suspended sentence in South Africa in 2005 for his involvement in the coup.
He has always claimed he was an unwitting conspirator and that, as far as he knew, he was helping finance a new company - an air ambulance business in West Africa.
Equatorial Guinea, an oil-rich former Spanish colony, has been ruled by President Obiang since he seized power from his uncle in 1979.
His government has been accused of widespread human rights abuses and of ruthlessly suppressing political opposition.
Transparency International has put the tiny nation in its top 10 corrupt states.