Scott Smith admitted punching the renowned chef, who runs a cookery school and pizza restaurant in the city, on the head in Union Street on 22 December.
The 35-year-old, from Aberdeen, was fined £900 on Monday by Sheriff Raymond McMenamin at the city’s sheriff court.
Nairn tweeted a picture of his injuries following the attack as police launched a hunt for his attacker. Smith was arrested days later and released on an undertaking to appear at court.
Speaking after the assault, Nairn told how his partner tried to strike Smith with her handbag as the chef lay injured on the ground.
The 58-year-old said: “She was hitting the guy with her handbag. She’s a real have-a-go hero. I remember watching her thinking ‘Christ almighty’, you wouldn’t cross her.”
Police carried out tests on the handbag in the hope it might have picked up some DNA.
Nairn had been walking back to his hotel following a visit to his Aberdeen restaurant when the altercation took place.