Mozambican President Arnando Guebuza has signed a peace deal with ex-rebel leader Afonso Dhlakama, who on Thursday emerged from two years in hiding.
President Guebuza hailed the deal to end a low-level insurgency as "a very important day for our people".
Mr Dhlakama agreed but also accused the government of "intolerance", the AFP news agency reports.
The head of Renamo, which fought a 1975-1992 civil war, says he will contest next month's elections.
He has contested every poll since the civil war ended but has always lost.
Mr Dhlakama flew into the capital Maputo on Thursday accompanied by diplomats, after a deal to end the conflict was agreed last month.
After signing the deal, he said he hoped it "can bring to an end the one-party state", AFP reports.
"After the beautiful dream of two decades ago when peace seemed to be for always, we saw a systematic concentration of power in the hands of those in power... many are in this room," he said, drawing gasps and mutters from the audience, according to AFP.
The Renamo leader went into hiding in October 2012, after accusing the government of breaking the terms of the 1992 peace deal.
The conflict threatened the economic progress Mozambique had made in recent years.
Presidential and parliamentary elections are due on 15 October.
Mr Guebuza is stepping down after serving two terms and former Defence Minister Felipe Nyusi will be the candidate of the governing Frelimo party.