Gerrard Scanlon, 53, was arrested after Sky Sports News broadcast footage which appeared to show some of the London club's supporters abusing Senegalese striker.
The delivery driver admitted unleashing a foul-mouthed tirade when he was brought before magistrates on Thursday morning and fined £425.
He was told to pay further costs of £85 and a £15 victim surcharge, Scotland Yard said.
The club issued the following statement: "Millwall Football Club understands Gerrard Scanlon, the man caught in the recent Sky Sports News documentary uttering racist abuse at a Leeds United player, appeared at Bromley Magistrates Court on Wednesday morning.
"The club had already decided to ban Scanlon for life from all matches at The Den.
"We are pleased that the behaviour of this individual came to notice, and that the police and the courts have now taken action against him.
"Millwall Football Club will continue to operate a zero tolerance policy to target and ban any fan guilty of displaying racist behaviour, and we look forward to developing even closer links with other agencies, including those in the media who share our determination to eradicate racism from our game."