The man, who had been drinking, did not gain access to the palace.
He was not armed and no Taser was deployed by officers.
The man is currently in custody at a central London police station. The breach is not believed to be terrorism-related.
The Queen and the Duke of Edinburgh were not at Buckingham Palace at the time.
Each summer Elizabeth II travels to the Scottish royal home of Balmoral. Buckingham Palace declined to comment on the matter.