On Monday an Ethiopian court rejected a prosecution attempt to sentence leaders of the Coalition for Unity and Democracy (CUD) to death, and handed life sentences to 35 of them.
Eight other defendants were given sentences of between 18 months and 18 years.
The sentences, which followed a nearly two-year-long trial, were immediately met with criticism from human rights groups.
The United States, a close ally of Meles, urged clemency.
The defendants were tried after two post-election bouts of violence in which 199 people were killed, 800 wounded and 30,000 arrested, according to a parliamentary inquiry.
Meles said: "We believe that the sorry saga of the orange revolution is fully behind us."
The return of their constitutional rights means the imprisoned CUD members, among them elected legislators and the mayor-elect of Addis Ababa, the Ethiopian capital, can run for election again.
It was not immediately clear if those who had won seats would be able to take them up after their release.
They were released from Kaliti prison on the outskirts of Addis Ababa on Friday.
Meles said: "The decision to pardon the CUD members also conveys that there is no sense of revenge by the government."
The prime minister denied influence from Washington, which considers Ethiopia its strongest ally in the 'war on terror' in the Horn of Africa, had played any role.
Meles said: "The Ethiopian government isn't willing and is unable to be run like a banana republic from Capitol Hill. Some individuals appear to be entertaining such illusions."
It was unknown whether the remaining people convicted in the case, among them opposition members, journalists and human rights activists, would be pardoned.
The government has said the clemency appeal of the remaining prisoners out of the 72 convicted would follow, as well as those who are in exile and were tried in absentia.
The clemency appeal was completed in just five days after the CUD leaders sent a letter admitting their guilt and pledging to respect the law.
The government made the letter public on state television on Monday, hours after the sentences were handed down.
However, Hailu Shawel, Ethiopia's opposition leader, condemned the government, just hours after his release.
Hailu said he had signed the apology under duress and that he had no apology to make for protesting against the 2005 election results because "for us it is a normal political protest."
He said the government had failed to fulfil all the conditions agreed with mediators for the release of the opposition politicians and activists, such as allowing them take their seats in parliament.
Hailu said: "As a leader you have to compromise somewhere along the line. But the government has already reneged on what they said."