"We hope to participate with them in a battle that they lead. They hold the banner and we stand alongside them as supporters," Gulbuddin Hekmatyar said in the tape.
A warlord allied with the Taliban, Hekmatyar was Afghanistan's prime minister from June 1993 to June 1994. His faction, the Hezb-e-Islami, helped end the Soviet occupation of Afghanistan. The Taliban chased him out of Kabul in 1996.
His group has been blamed for several recent attacks against U.S.-led coalition forces in Afghanistan.
Some 2,500 U.S. and Afghan soldiers have been waging a campaign for the past four weeks in rugged eastern Afghan terrain bordering Pakistan.
It is thought that the network of support that Hekmatyar commands in Afghanistan could shelter Bin Laden and other Al Qaeda leaders.
The Pakistani Interior Minister Aftab Khan Sherpao said last month he believed bin Laden and his number two, Ayman al-Zawahri, may be hiding in eastern Afghanistan near the Pakistani border. Parts of eastern Afghanistan are controlled by Hekmatyar.
Thursday's tape appeared less than two weeks after three Al Qaeda leaders issued messages in quick succession.
Wearing a black turban, eyeglasses and sporting a long white and gray beard, Hekmatyar said: "If it weren't for the Pakistani and Iranian support, the Americans wouldn't have been able to occupy Afghanistan and Iraq as quickly and as easily."
Al-Jazeera did not say how it received the tape and it was not clear when it was made.
He spoke against a plain gray backdrop with an automatic rifle leaning against the wall beside him.
Hekmatyar has issued videotapes previously, but not since 2004.