Bridget Seisay, 30, from east London, who was acquitted at the Court of Appeal in Brussels, had spent eight months in jail after being convicted of trafficking in humans.
She is expected to return immediately to Britain to be reunited with her two-year-old son and husband.
Her prosecution and imprisonment had been branded racist by civil rights organisations and lawyers in Britain.
Ms Seisay, originally from Sierra Leone, was arrested at the Eurostar rail terminal in Brussels last November as she accompanied a female acquaintance boarding the train to London. Her British passport was in order but her companion, it transpired, was travelling with false documents.
Ms Seisay was arrested and charged with attempting to smuggle the woman into the country. Although the woman was subsequently released, Ms Seisay was imprisoned.
She had met her travelling companion during a weekend in Bonn with her husband'scousin, Umaru Wurie, the Sierra Leonean ambassador to Germany.
Ms Seisay's husband, Habib Tejan, said his wife had been imprisoned solely on the basis of "supposition, without a single scrap of evidence".
He described her treatment as a "travesty of justice" and said the family was considering taking action against the Belgium authorities for wrongful imprisonment. He added: "The family will now try to return to normal, quiet family life again as soon as possible."
Stephen Jakobi, of the Fair Trials Abroad pressure group which took up Ms Seisay's case, said mistakes had been made in the handling of the case which should be investigated.
"There should be an inquiry into what went wrong in the lower reaches of the Belgium judicial system that could leave this person in prison for over seven months," he said.
Mr Jakobi said he was delighted that Ms Seisay had been released. "There is total relief that the misery inflicted on this family as well as the enormous stress, is at an end and they can begin to rebuild their lives."
Ms Seisay's MP, Simon Hughes, and the London MEP Richard Balfe had also expressed concerns about the case and the Belgian ambassador to the UK intervened urging the case to be heard as soon as possible.
A spokesman for Mr Hughes' office said that many lawyers thought the case had a racist element.
Mr Hughes said: "The Belgian government knows of my concern that this case is being seen, particularly by members of the ethnic minority, as a test of the fairness of the Belgian legal system."
A Belgium-based pressure group, the Campaign for Open Politics in Europe, had also taken up the case.
Nick Orbaen, spokesman for the British Embassy in Brussels, said yesterday that Ms Seisay was free to leave Belgium. He said: "I can confirm that she has been acquitted of all charges by the Court of Appeal in Belgium and is expected to return to the UK as soon as possible after being released from prison today."Reuse content