Goddard was convicted of the offence after Manchester Magistrates’ Court heard he grabbed at Joel Goodman’s camera as he covered the protest in the city centre.
He was cleared of using threatening words or behaviour to cause his victim to fear “immediate” violence at the same rally on 9 February this year.
As Mr Goodman entered the witness box to give evidence in Tuesday's trial, Goddard surreptitiously held up a piece of paper on which he had written: ”Pussy coward leftist soy boy.”
Police officers were called into the court to seize the piece of paper and Goddard was warned he may be in contempt of court, but district judge Mark Hadfield chose to allow proceedings to continue.
After hearing evidence from both Mr Goodman and Goddard, the judge convicted the defendant of common assault.
Goddard was cleared of using threatening words or behaviour in relation to him telling Mr Goodman: “I swear to god when there’s no police around here, I’m going to take your head off your shoulders ... Your card is marked."
Goddard told the court his words were a “common English idiom”.
He was fined £300 for the common assault, and ordered to pay £500 in prosecution costs, £50 compensation to Mr Goodman, and a £30 victim impact surcharge.
The judge also imposed a two-year restraining order banned Goddard from approaching the photographer.
Goddard has been seen as the ringleader of the UK's "yellow vest" movement, which has seen right-wing activists block bridges in London and heckle politicians and journalists outside parliament.