Buckingham Palace is the official home of 91-year-old Queen Elizabeth II, the longest reigning monarch in British history.
Officers from the Metropolitan Police’s Royalty and Specialist Protection Command said the 24-year-old-man was arrested “within three minutes” on suspicion of trespass on Monday evening.
The suspect was not carrying any offensive weapons and “the incident is not being treated as terrorist-related”, the police said in a statement.
“He was also arrested on suspicion of being in possession of a controlled substance for which he was subsequently released with no further action,” police said.
According to the police, the suspect has undergone a mental health assessment and was released on conditional bail, only to return to a central London police station early next month.
A number of people have tried to get unauthorized entry into the palace grounds in recent years.
In August, a 26-year-old sword-wielding man attacked and wounded three police officers outside Buckingham Palace before being arrested.
A woman was arrested in October for attempting to scale the gates of the palace.