The “combat” weapon was carried by teenager Shaquille Powell Anderson, from Birmingham.
Anderson, 19, was arrested on Portland Street after members of the public called police when they saw him with the huge blade near Burger King in Piccadilly Gardens.
He was arrested by Greater Manchester Police on a Wednesday afternoon last month.
Manchester Evening News reports he was with four other men. CCTV operators traced them as they moved near the Britannia Hotel.
Anderson, who has been previously stabbed, told officers he had a knife in his waistband, prosecutor Rachel Widdicombe told Manchester Crown Court.
Sentencing him to 20 months in a young offender institution, Judge Richard Mansell QC said the knife was ‘clearly very dangerous’ and ‘a really serious weapon to be carrying in public’.
“This was a very dangerous knife,” he said.
“You clearly possessed it in public, otherwise the public wouldn’t have phoned the police.
“There was risk you were thinking of using it.”
Part of his sentence was imposed after he admitted breaching a suspended sentence he previously received for his role in a ‘county lines’ drug plot.
Anderson and other men took over the home of a vulnerable man in Warrington, living there and using it as a base to sell heroin and crack cocaine.
Defending, Alistair Reid said Anderson acted as a ‘gofer’ for the gang.
At Liverpool Crown Court, he received a 16 month suspended sentence for possession with intent to supply drugs.
Mr Reid said Anderson had previously been the victim of a stabbing.
“If anyone was aware of the dangers and the risks that the possession of knives carries, he is well aware of that,” the barrister said.
Mr Reid said Anderson, of Hastings Road, Birmingham, wants to put his crimes behind him and he wants to ‘move forward with his life’.
But the judge said: “It is clear that you have decided to carry on mixing with other pro-criminal associates.
“It’s the only explanation for you being in Manchester and in possession of that knife.”
Judge Mansell urged Anderson to ‘get yourself back to Birmingham’ and ‘back to college’ after he is released.