The far right leader, who is a Member of the European Parliament, had been invited along with 8,000 other guests to the event which is being hosted by the Queen and attended by the Duke of Edinburgh.
But officials withdrew the invitation after warning his attendance could increase the security threat and cause discomfort for others attending.
A Palace spokesman said: “Nick Griffin MEP will be denied entry to today's Garden Party at Buckingham Palace due to the fact he has overtly used his personal invitation for Party political purposes through the media
“This in turn has increased the security threat and the potential discomfort to the many other guests also attending.
“Mr Griffin's personal invitation was issued to him as an elected Member of the European Parliament. The decision to deny him entry is not intended to show any disrespect to the democratic process by which the invitation was issued.
“However, we would apply the same rules to anyone who tried to blatantly politicise their attendance in this way.”
Other members of the Royal Family who were due to attend the event included the Duke of York, The Duke and Duchess of Gloucester and the Duke of Kent.
Mr Griffin described the decision as "an outrage" and "thoroughly anti-British".
The BNP leader said: "This is quite amazing news. At no time was I informed that I wasn't allowed to talk to the media about this. Other people have talked about attending. Why a double standard here?
"To say that one person in the country cannot speak to the media is an outrage."
Asked if he still intended to go to the palace, Mr Griffin initially said: "I don't know."
But he then added: "I'm not about to try and gatecrash the party, that is for sure."
Mr Griffin said he did not "blame the Queen" and claimed Buckingham Palace was under "enormous pressure from the Lib Con coalition" to withdraw his invite.
He maintained he had a mandate from a million British people and had a right to attend.
The BNP leader added: "I am held to a different standard to everyone else in the country - that is thoroughly anti-British."
A Buckingham Palace spokeswoman said later that BNP MEP Andrew Brons's invitation to today's garden party had not been revoked as he had not "exploited" it for political ends.
But Mr Griffin's guests - thought to be his wife and children - could not attend as he had been barred.
The Telegraph
