the new testament was written in Greek.
If your definition of "New Testament" is the Greek Septuagint, then yes, of course it was, and used as the source material for the KJV.
However, the above said, the first testimonies were written down/recorded in Hebrew as the evidence overwhelming supports. And even if they hadn't been, much of the Hebrew meaning would have still been lost in translating to Pagan Greek.
The New Testament was translated into Greek.
None of the disciples could speak Greek, they knew only their native Hebrew.
The Greek OT quotations were taken from the LXX and dubbed in over a century after the initial gospel was written by Cohen Matthew.