John Lennon's Killer Mark David Chapman -- DENIED PAROLE

The man who shot and killed John Lennon will remain behind bars ... at least for now ... because a NY parole board has DENIED his release.

Mark David Chapman -- who shot the famous Beatles member in front of Lennon's Manhattan apartment in 1980 -- has been serving 20 years to life for after pleading guilty to 2nd degree murder.

The 57-year-old went in front of a parole board today for the 7th time since the murder ... but New York corrections officials decided he is not ready to rejoin society.

MDC shot Lennon 4 times in front of his wife Yoko Ono on that fateful day. He later admitted he planned the killing because he wanted to become famous.