Harvey, 23, who was also ordered to pay prosecution costs of £2,852, blamed intense media pressure following his temporary sacking from the chart-topping group.
An idol to thousands of teenage girls, Harvey had been sacked after admitting taking 12 Ecstasy tablets on one night and saying the drug made "better people".
Shirt ripped off his back
Harvey, from Loughton, Essex, said he "snapped" when Reinaldo Vargas tried to get a picture of him emerging drunk from a top London nightclub. He, and four of his friends, pushed the photographer off his feet and began kicking him.
Southwark Crown Court was told Harvey lost his trainers and had his shirt ripped from his back as bouncers tried to keep him off Vargas, who was working for a tabloid newspaper.
He was arrested and handcuffed by a woman police sergeant as late-night revellers, queuing up to get into Stringfellows, laughed at his plight.
Harvey was acquitted of assault causing actual bodily harm; he had been accused of punching Mr Vargas in the eye, but was convicted on a count of affray.
Verdict shocked wife
The guilty verdict, coming after a week-long trial, clearly shocked his wife Natasha, 26, as well as fellow East 17 members John Hendy and Terry Coldwell, who were also in court.
Harvey's friend, Stephen Exley, 27, who admitted kicking the photographer once in the back, was also arrested.
He was fined £200 and ordered to pay a similar amount in costs.
Outside the court Harvey's solicitor Nigel Calvert said his client was very disappointed at the outcome of the trial.
He said: "Brian maintains that he did nothing wrong and stands by his claim made to the police that he walked into a trap set by the paparazzi, by which they have been rewarded handsomely and he has borne the consequences."
Judge criticises paparazzi
Passing sentence Judge Jeffrey Rucker criticised the paparazzi.
He said he had no doubt Harvey, Exley and their friends were not "looking for trouble" on the night.
He said the singer had agreed to let Mr Vargas and his partner John Bushell take photographs outside Brown's nightclub in London's West End earlier.
"But these gentlemen were not content with that. As I have learnt in this case they seldom are," said the judge.
He said: "They admitted quite frankly they worked as a pair because if one gets into trouble and is attacked, the other one can take pictures and that can be good for business."
Photograph was a lie
Judge Rucker also criticised a photograph of Mr Vargas used in a tabloid newspaper, showing him in bed wearing a neck brace and a sling.
Mr Vargas had not been seriously injured, suffering only a grazed forehead and a minor nose injury and was discharged from hospital with a few analgesics.
The judge said: "That photograph was a lie and the people who had anything to do with it should be ashamed."
Mr Vargas was paid £10,000 and his partner received £20,000 from the paper for pictures of the melee and its aftermath.
East 17 (unofficial)
Stringfellows
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