"I invite you to join the peace caravan and stop the pointless, meaningless and unholy war," Gulbuddin Hekmatyar said to a gathering of his followers and Afghan politicians in Laghman province, east of the capital, Kabul.
"I want a free, proud, independent and Islamic Afghanistan," he said.
In February the United Nations Security Council agreed to drop sanctions against Mr Hekmatyar, paving the way for him to return openly to Afghanistan.
The Afghan government requested the move as part of a peace deal with Mr Hekmatyar and his group, Hezb-i-Islami, in September.
Afghan President Ashraf Ghani welcomed Mr Hekmatyar's public return, saying the former strongman would cooperate with the government.
"Hezb-i-Islami leader Gulbuddin Hekmatyar's return will have remarkable effects on peace, stability, prosperity and development in all aspects," Mr Ghani's office said in a statement.
The deal has been criticised by some Afghans and human rights groups for the pardon it granted to Mr Hekmatyar and many of his followers.
Mr Hekmatyar's return 'will compound the culture of impunity', Human Rights Watch researcher Patricia Gossman said of the deal, calling it an 'affront' to victims of abuses.
A controversial figure from the fight against the Soviets in the 1980s and the civil wars of the 1990s, Mr Hekmatyar is accused of ordering his followers to bombard Kabul, leading to many casualties, besides other abuses.
His faction of Hezb-i-Islami has played a relatively small role in the current conflict, in which the Taliban have a leading role in battling the Western-backed government in Kabul.
In hiding for nearly a decade and a half, Mr Hekmatyar had been designated a 'global terrorist' by the United States, which has been leading an international military mission in Afghanistan for the past 15 years.
American and other Western leaders praised the deal with him, however, hoping it could help lead to wider peace in Afghanistan.
(Writing by Josh Smith, Editing by Clarence Fernandez and Muralikumar Anantharaman)