Susan Hull, the dead soldier's widow, said that her family felt the verdict was correct.
"There have to be lessons learnt," she said. "It's very clear that after such a death evidence is required - full evidence, right from the beginning.
"If that doesn't happen in circumstances like this then this will all have been in vain," she said.
The inquest, in the southern England city of Oxford, heard the pilot of one of two US A-10 "tankbuster" planes opened fire on Hull's clearly-marked armoured vehicle convoy in southern Iraq on March 28, 2003.
Hull, a 25-year-old British soldier, died and four other soldiers were injured in the attack.
Britain's defence ministry initially said cockpit footage of the incident did not exist, and the US later refused to release it when it did emerge.
The hearing made headlines around the world after the British Sun newspaper secured a leaked copy of the classified recording. It was later broadcast on television.
"The pilot who opened fire did so with disregard for the rules of engagement and acting outside the protection of the law of armed conflict... I don't think it was a case of an honest mistake"
Andrew Walker, coroner
The pilot of one of the US jets said after realising their mistake: "We're in jail, dude."
The other, who opened fire, was heard weeping and saying: "Goddammit."
Walker has criticised the US military's refusal to co-operate with the inquiry. The Pentagon refused to accede to requests from the British government to send a representative to the inquiry.
US policy is to send a statement, not witnesses, to such inquests.
As the verdict of unlawful killing was reached, it also emerged that the US failed to provide a full version of its investigation into the incident and had turned down a request to give details of its rules of engagement.
Susan Hull wanted George Bush, the US president, to help the inquiry by producing 11 censored lines from an interview between a ground controller and one of the pilots.
In the recording, the pilots are heard convincing themselves that the orange panels on top of Hull's convoy, which marked them out as coalition forces, were Iraqi rocket launchers.
Walker said on Friday: "The pilots chose not to take steps to confirm the identity of the vehicles in the convoy that they could easily have taken.
"The pilot who opened fire did so with disregard for the rules of engagement and acting outside the protection of the law of armed conflict... I don't think it was a case of an honest mistake."
Geraldine McCool, Susan Hull's lawyer, said the unlawful killing verdict did not mean the US pilot could face a criminal prosecution, nor would they be seeking it.
No disciplinary action was taken against the pilots, from the Idaho Air National Guard, by the US military.