The return of Hekmatyar, a former prime minister, comes eight months after the government signed a peace deal with representatives of Hezb-e-Islami -- the insurgent faction led by the warlord.
Hekmatyar's convoy, complete with luxury SUVs loaded with heavily armed men, drove almost 200 kilometers from Nangarhar Province to Kabul on Thursday.
Dozens of Kabul residents gathered along the streets as he arrived, with some chanting, "Long live Hekmatyar." He then met with Afghan president Ashraf Ghani. He was expected to address a mass rally Friday at Kabul's Ghazi Stadium, Tolo reports.
The warlord's return is a symbolic moment and is "likely to send chills through the hearts of the many Afghans who endured rocket fire and worse from Hekmatyar's forces," says CNN's Ivan Watson.
Kabul resident Mohammad Barakzai lived through those attacks, and he told CNN that the carnage eclipsed anything else he had witnessed.
"I have seen much war in Afghanistan, but war at the time of Hekmatyar was the worst in the history of Afghanistan," the 47-year-old said. "The Afghan people will never forget those days. Hekmatyar has killed thousands of innocent people by hundreds of rockets in Kabul city."
Hekmatyar's arrival follows the signing of a peace agreement in September, which granted him immunity
for acts committed during the war -- as well as the removal of his name and Hezb-e-Islami from terrorism blacklists. In return, Hezb-e-Islami will renounce its ties with extremist groups.
At the time, Afghan and US officials applauded the peace agreement, which the US Embassy said was "a step in bringing the conflict in Afghanistan to a peaceful end."
US-based NGO Human Rights Watch
said the deal compounded a "culture of impunity" surrounding the warlords who devastated large swaths of the country in the 1990s.
"Hekmatyar bears responsibility for some of the most egregious incidents (during the fight for Kabul), including barrages in August 1992 that killed at least 1,000 people and wounded 8,000, according to the International Committee of the Red Cross," said Human Rights Watch's senior researcher Patricia Gossman.
CNN's Watson said it was still unclear whether the peace deal can "seriously tilt the US-backed Afghan military's fortunes on the battlefield against the Taliban."
"The Taliban controls vast swaths of Afghan territory and is seriously contesting far more land," he said.
Gulbuddin Hekmatyar is one of the most well-known and feared warlords in Afghanistan's bloody history of more than three decades of conflict.
As a mujahideen commander in the 1980s, he received some $600 million in US aid, as Washington armed Afghan fighters battling the Soviet occupation.
After a brief stint as prime minister in Afghanistan's post-communist government in the 1990s, Hekmatyar was one of several former mujahideen warlords directly responsible for destroying large parts of the Afghan capital in the vicious power struggle to take control of Kabul.
Some residents nicknamed the warlord "Rocketyar" for his faction's frequent rocket strikes on the city.
Hekmatyar came out quickly against the US-backed overthrow of the Taliban in 2001. His fighters are accused of deadly attacks against US forces in Afghanistan.
Some analysts argue Hekmatyar -- who commands a following within Afghanistan's ethnic Pashtun community -- might serve as an important ally for president Ghani.
Ghani faces simultaneous challenges from the Taliban as well as from other ethnic leaders represented within his government who command their own powerful militias.