The High Court has blocked the Home Office's decision to deport a convicted drug dealer to Jamaica.
The court ruled the man can make a fresh application to stay in the UK as he was a reformed crack cocaine addict.
The judge added the Home Office had not sufficiently looked at the effect on his nine-year-old son who suffers from attention deficit hyperactive disorder.
The Home Office said he had a history of violence and his removal would be "conducive to the public good".
An immigration judge rejected his appeal against deportation in 2006.
The judge had said at the time there was nothing to prevent his wife and son from joining him in Jamaica, and the public interest in the father being deported outweighed the compassionate circumstances of his case.
But on Monday, Mr Justice Collins said the fresh claim was based on Parole Board reports not seen by the immigration judge that showed he had "learned his lesson", was in employment and no longer involved in drugs.
He ruled the Home Office had wrongly rejected his application to bring a fresh human rights claim to be allowed to stay with his family in the UK.
Mr Justice Collins said the son, who must not be identified for legal reasons, had been described by his north London school as "one of the vulnerable group of black Caribbean boys" for whom absentee fathers was one of the main causes of educational weakness.
The Home Office said the public interest in deporting him outweighed his family rights under Article 8 of the European Convention on Human Rights.
The Home Office said it was through engaging in drug crime and his own actions that he was an absentee father and jeopardised his right to remain in the UK.