European judges in Strasbourg are set to make a final ruling on whether prisoners should be allowed to vote.
John Hirst is confident that European judges will back his view
The government is appealing against an earlier verdict that current British laws barring prisoners from voting breach human rights.
The original result was a victory for ex-prisoner John Hirst, who was awarded £8,000 in costs and expenses by the European Court of Human Rights.
British law bars convicts from voting in parliamentary and local elections.
This is made clear in the 1983 Representation of the People Act.
The High Court rejected Mr Hirst's assertion that Section 3 of the Act is incompatible with the European Convention on Human Rights, to which Britain is a signatory.
But the former inmate won his case in the Human Rights court in Strasbourg, where his lawyers successfully argued that prisoners should have the right to vote under the Convention's guarantee to the "right to free elections", the "right to free expression" and "prohibition of discrimination".
And judges delivered a unanimous verdict that denying a prisoner a vote does breach the "right to free elections" set out in the Convention.
If the original verdict is upheld by the court's 17-judge Grand Chamber in their final judgement, current law will have to be changed to ensure that all prisoners in Britain can cast their vote if they wish to do so.
Mr Hirst, 54, was released last November from a life sentence in Rye Hill prison, Warwickshire, where he had been held for manslaughter.
"When I was in prison I wanted to vote and I was surprised to find I couldn't," said Mr Hirst, who now lives in Hull.
"I took it up with the authorities. When I lost my case in Britain I was advised I had a good chance if I went to the Human Rights court."
The former inmate went on: "The government has argued that prisoners who are in jail have given up their right to vote by their criminal actions, but the Human Rights court has already unanimously said that that position is wrong.
"It doesn't matter how heinous the crime; everyone is entitled to have the basic human right to vote."
He is confident the Grand Chamber will confirm their previous ruling in the final round of the legal battle.
In 1980 Mr Hirst pleaded guilty to a charge of manslaughter on the grounds of diminished responsibility and was sentenced to "discretionary life imprisonment".
The tariff part of his term - the part relating to retribution and deterrence - expired in June last year.
However, he was not freed until five months later.