Unbeknown to him, hovering high above was an MQ-9 Reaper “hunter-killer” drone, remotely piloted from a US base.
The $US64 million ($92 million) drone, with a 20-metre wingspan, circled silently and waited for him to emerge.
Soleimani was greeted by Abu Mahdi al-Muhandis, an Iraqi militia commander with the Popular Mobilisation Forces (PMF).
Muhandis pulled up to the aircraft steps in two cars and Soleimani got in.
Also in the cars were Mohammed Ridha Jabri, the PMF public relations chief, and eight others.
Moments later, the vehicles passed through a cargo area and headed for an access road leading out of the airport.
The drone swooped in, unleashing four missiles, which struck the targets, killing all the occupants. Pictures taken by drivers passing on a nearby road showed the wreckage still burning next to a concrete wall.
The bodies of Soleimani and the others were badly mutilated but he was quickly identified by a distinctive red ring on his finger.
Trump had spent the days before the audacious strike holed up in unusual seclusion at Mar-a-Lago, eschewing public appearances and mulling over his response to recent Iranian-inspired attacks on the US embassy in Baghdad.
He was believed to have seen photographs of graffiti left by rioters at the embassy, in which they pledged allegiance to Soleimani.
Trump began consulting with trusted advisers early in the week about how to respond.
That included Lindsey Graham, the senator and Iran hawk, who was spotted playing golf with the President and later confirmed he had been briefed ahead of the strike.
Trump’s mind was made up after he was briefed that Soleimani was planning what US intelligence officials called a “significant” action against US interests, with the potential to kill hundreds in Iraq, and possibly elsewhere.
The US had been tracking Soleimani’s movements for years, using sophisticated electronic surveillance.
The best opportunity in a while to neutralise him came as his plane arrived at Baghdad airport, from either Lebanon or Syria. US intelligence had learnt of the trip through a combination of highly classified information from human sources, electronic intercepts and reconnaissance aircraft.
Trump had warned on Twitter in recent days that Iran would “pay a very BIG PRICE!” for the embassy siege, and that he was making a “threat”.
But, according to US officials, Soleimani had become blase and his convoy had little security.
Bill Roggio, a senior fellow at the Foundation for Defence of Democracies in Washington, said: “US military officials and officers have told me that they have been able to track Soleimani for years.
“He became careless and complacent as his influence in Iraq grew. His actions indicate he felt the US would never target him.”
Previous US presidents had decided against killing him, fearing the potential repercussions in the Middle East. As part of the Iranian state apparatus, he represented a very different prospect than terror leaders Osama bin Laden or Abu Bakr al-Baghdadi.
However, Trump, and Mike Pompeo, the US Secretary of State, had become increasingly keen to neutralise him.
The intelligence that Soleimani was planning a major attack, meant his killing could be justified as a “defensive action” by the US.
But analysts warned that the assassination would now plunge the region into the unknown.
Charles Lister, a senior fellow at the Middle East Institute, said: “The killing of Qassem Soleimani is one of the biggest developments in the Middle East for decades. It far eclipses the deaths of Bin Laden or Baghdadi in terms of strategic significance and implications.
“With Soleimani dead, war is coming – that seems certain, the only questions are where, in what form and when?”
America was split over Trump’s decision as it braced for Iranian revenge attacks.
Marco Rubio, the Republican senator, said Trump had “exercised admirable restraint while setting clear red lines and the consequences for crossing them. Iran chose the path of escalation”.
But Joe Biden, the Democrat presidential candidate, accused Trump of “tossing a stick of dynamite into a tinderbox”.
The most fervent opponents of Iran in Washington pressed the White House to make the death of Soleimani a step toward regime change.
But officials familiar with Pompeo’s thinking said that he hoped the general’s demise would lead to “behavioural change” by the Iranian regime, and ultimately a de-escalation of tensions.
In Iraq, some residents of predominantly Shiite areas in Baghdad and Basra were seen cheering the death of the man they accuse of ordering the killing of hundreds of protesters in both Iraqi cities in recent weeks.