The immunity is part of a national stability plan that says that "all those political and belligerent sides who were involved one way or the other during the 2 1/2 decades of war will not be prosecuted legally and judicially."
Both critics and supporters of the move say it covers fugitive Taliban leader Mullah Mohammad Omar and former prime minister Gulbuddin Hekmatyar -- who now heads his own militant group.
Mohammad Mohaqeq -- a former mujahedin leader and one of the key legislators behind the amnesty -- told RFE/RL's Radio Free Afghanistan today that it is an attempt to bring peace and reconciliation to Afghan society.
"This was approved [on January 31] with an absolute majority of votes," said Mohaqeq, who finished third among 18 names on the Afghan presidential ballot in 2004. "It mainly says that all of those who were involved in the 2 1/2 decades of war, should [work] together and join the national reconciliation."
But human rights groups say bringing war criminals to justice -- including some members of parliament and senior government officials -- is vital for peace.
The stability plan passed by legislators dismisses a Human Rights Watch report chronicling past abuses by senior public figures as "inaccurate" and "baseless" and the result of "malicious intentions."
Afghan independent Tolo Television quoted Kabul lawmaker Abbas Nuyan questioning the legislature's authority to extend such an amnesty. "You do not have the right," he said, adding that "the rights of hundreds of thousands of people have been violated in Afghanistan."
(with additional reporting by Reuters and Tolo Television)