David Booth, 54, attacked Catherine Byrne in the Storm Queen pub on Glasgow's Dumbarton Road on 2 January.
Booth, from Dunfermline, admitted biting Ms Byrne's lower lip to her severe injury, permanent disfigurement and permanent impairment.
Glasgow Sheriff Court heard the victim's lip was reconstructed by stitching the outer edges of her wound.
Jailing Booth, Sheriff Ian Miller told him: "It was a single horrible and repellent act."
He also placed Booth on a non-harassment order for three years meaning he cannot contact or attempt to contact Ms Byrne during that time.
The court heard that Booth and Ms Byrne met on a dating website and had been in a relationship for around a year before she ended it due to him constantly attempting to monitor her movements.
On 2 January, she put his possessions on her porch and made arrangements for him to collect them.
That night Booth stopped off at her home and told Ms Byrne he wanted to get back together.
She refused although invited him out for a drink with her.
The court heard they went to a pub in Anniesland then to the Storm Queen pub in Partick.
A bouncer told the court he saw Booth being aggressive towards Ms Byrne and her move away from him to sit with a group of others.
A short time later Ms Byrne was dancing when Booth approached her.
When she tried to push him away he grabbed her by the shoulders and bit her bottom lip and spat it out on the floor.
Ms Byrne screamed: "He bit my lip, he bit my lip" as blood poured from her face. She yelled to get Booth away from her and he was escorted out of the pub.
When police and paramedics arrived an officer saw "a piece of  lip" on the floor and gave it to ambulance staff.
Ms Byrne was taken to the Western Infirmary then the Southern General where she had surgery the following day.
Part of her lip was missing and another part cut away and her lip reconstructed by stitching the outer edges.
The court heard she struggles to form certain letters and suffers numbness in her lip and the injury has resulted in her drooling from the right side because of a gap.
A man who bit off his ex-partner's lip after he saw her talking to another man in a bar has been jailed for 27 months.