The order will come into effect tomorrow and make it a criminal offence to be a member, punishable by up to ten years in prison.
Mr Johnson said the group had tried to escape proscription by changing its name.
"It is already proscribed under two other names – Al Ghurabaa and The Saved Sect," he said.
"Proscription is a tough but necessary power to tackle terrorism and is not a course we take lightly. We are clear that an organisation should not be able to circumvent proscription by simply changing its name."
The law to ban the group is made in a parliamentary order that was laid in the House of Commons yesterday. It is an extension of an existing order made under the Terrorism Act 2000 that bans the group under the name Al Ghurabaa and The Saved Sect.
Islam4UK is led by Anjem Choudary, who founded Al Muhajiroun in the 1980s with radical cleric Omar Bakri Mohammad.