Like many of the Taliban's top leadership, Baradar is an enigmatic figure. He is not thought to speak English and does not court the media, restricting himself mainly to official statements laced with Quranic quotes.
But while he was picked for negotiations because he is seen as one of the group's more politically pragmatic operators, his words carry more than a hint of menace. Before his arrest in 2010, he masterminded a ruthless Taliban terror campaign that targeted not only Western forces but also any Afghan who co-operated with the civilian government.
In a video message released on Sunday, in which he praised the "unexpectedly swift" Taliban take-over, Baradar promised to "serve the Afghan people and set an example for the rest of the world".
A look at his past life, however, reveals little to suggest his "example" will be anything other than a return to the harsh religious orthodoxy of the Taliban's previous rule in the 1990s.
Born in Afghanistan's central Uruzgan province, he is said to have fought with the mujahideen against the Soviets before becoming one of a handful of men who founded the Taliban in 1994. He is thought to be married to the sister of the one-eyed Mullah Omar, the movement's late spiritual leader.
At the time of the US-led invasion in 2001, Baradar was serving as the Taliban's deputy defence minister. After the movement's collapse, he is rumoured to have been part of a Taliban faction that sought conciliation with Hamid Karzai, the US-backed president, who belonged to the same Popalzai tribe.
By 2008, however, Baradar was spearheading a vicious Taliban military comeback, devising a strategy known as "Ibrat" – meaning warning – that emphasised targeted killings, kidnappings and the use of suicide bombers, aimed particularly at Afghans serving in the Western-backed government.
Two years later, he was arrested in a joint operation between the CIA and Pakistan's intelligence services, who are said to have found him "accidentally" during a raid on a house in the port city of Karachi.
He was released in 2018 at the request of Zalmay Khalilzad, the US envoy to the then president Donald Trump. Mr Khalilzad is said to have believed that Baradar would be willing to settle for a power-sharing arrangement in Afghanistan, despite some scepticism among other US officials.
While another Taliban cleric, Mullah Haibatullah Akhundzada, serves as the Taliban's overall spiritual leader, Baradar assumed day-to-day political command, liasing with the group's "shadow governors" in Afghanistan.
Exactly what his vision for Afghanistan is will be is hard to predict. While some say the Taliban have modernised a little in recent years, reports on the ground in recent weeks talk of them continuing bans on women's education.
Graeme Smith, a Canadian journalist who met the Taliban negotiating teams in the Qatari capital, Doha, told The Telegraph: "When our film crew sat down with Baradar's political advisors in Doha, I was struck by their willingness to engage with the outside world. This is a new generation of Taliban that wants recognition and support from the international community.
"At the same time, the Taliban still profoundly disagree with the Western world about basic concepts of democracy and human rights. It's fair to expect they will impose their own vision on the new Afghanistan and it will be breathtakingly different from our own."
In February last year, Baradar signed a peace agreement with the US, hailed at the time by the Trump administration as a diplomatic triumph.
That year, he also met Mike Pompeo, Mr Trump's Secretary of State, who – publicly at least – seemed confident that America could now treat its old foe as a working partner of sorts and declared: "We welcome the Taliban's commitments not to host international terror groups including Al-Qaeda."
With Baradar now poised to take power by force, that is just one of many "commitments" that could now be in question.
Who runs the Taliban?
Sirajuddin Haqqani
Deputy leader of the Taliban and an overseer of combat against Western forces in Afghanistan. Leader of the Haqqani network, a subset of the Taliban organisation with close ties to Al-Qaeda. Admitted responsibility for the 2008 bombing of Kabul's Serena Hotel, which killed six people, and plotting to assassinate Hamid Karzai, the then Afghan president.
Mullah Mohammad Yaqoob
The son of Mullah Omar, the one-eyed spiritual leader of the Taliban, who died in 2013. Now heads the group's military commission, in charge of field commanders. Enjoys considerable status thanks to his father's name. Seen as a unifying figure in a movement where fighters are often bound by blood ties and marriage.
Suhail Shaheen
The Taliban's main international spokesman. Fluent in English. Edited the Kabul Times, the government run English-language newspaper, during Taliban rule in the 1990s. Has promised in recent days that Afghanistan will have an "open, inclusive Islamic government" under its return to Taliban rule.
Khairullah Khairkhwa
Former Taliban governor of the western Afghan city of Herat. Spent 12 years as a prisoner in Guantanamo Bay, before being one of five Taliban prisoners released in a controversial exchange for Bowe Bergdahl, a kidnapped US soldier. Since appointed to the Taliban negotiating team in Qatar.
