The shopkeeper - known only as "ZR" - won his case to be granted entry on human rights grounds after a paperwork error by the Home Office department.
According to papers released by the immigration tribunal, he married a British woman in March 1998 and they had three children, all UK citizens.
In 2011, ZR applied to the Home Office to come and join his family, but was refused on the grounds that his admission was "not in the public interest".
The lower immigration tribunal then backed his case under Article 8 of the European Convention on Human Rights, which protects the "right to private and family life".
Although Government lawyers could still appeal that to a higher authority, they failed to lodge the papers in time.
Refusing permission to accept a late appeal in the upper tribunal, Judge Peter King said: "I find that the application is out of time without any clear explanation for being out of time."
Conservative MP Dominic Raab said: "It is a damning indictment of Labour's Human Rights Act that a double murderer can claim a right to family life to skip past UK border controls designed to protect the public."