Stephen Gervis, 39, of New Street, Cambridge was on Parkers Piece on 8 November when he was seen by an off duty special constable pushing and shoving a man and a woman.
He was then seen on CCTV to take a three-inch kitchen knife from his pocket and threaten and stab a man.
Gervis was arrested by firearms officers at the scene and was sentenced to 12 months and four weeks in prison at Peterborough Crown Court on Tuesday (15 December) after pleading guilty to common assault and threatening a person with a bladed article in a public place.
PC Matthew Walshe said: “Gervis publicly assaulted his then-partners and drew a knife on two men who tried to intervene. Safeguarding victims of domestic abuse will always be a priority for Cambridgeshire Constabulary and this case shows that those who continue to pose a danger can expect a prison sentence.”