Robert Chester, 38, was sentenced to a 12-week prison sentence, suspended for 12 months, and was also banned from attending football matches for three years.
The incident occurred as Derby County faced Sheffield Wednesday at Pride Park in Derby on Saturday, October 21 last year.
The Star has previously reported how fighting broke out among a small section of Wednesday fans during the match, which resulted in a 2-0 defeat for the Owls.
Speaking after the hearing at Derby Magistrates Court last month, PC Roger Brown of the Derbyshire Football Unit said: “This was one of the worst incidents of missile throwing I have seen in a football ground. It is pure luck that the steward who was hit by the seat wasn’t seriously injured.
“I hope the sentence and banning order handed to Mr Chester acts as a deterrent to others in the future.”
Chester, of Vessey Road in Worksop pleaded guilty to assault and throwing an object at a football match during the hearing.
He was also ordered to pay Â£200 in costs and told to complete a rehabilitation activity programme.