Prewitt, 68, had been on leave since 2013 following a diagnosis of brain cancer, Bloomberg said.
He joined the news service in 2005 after a radio and TV career that took him to the Wall Street Journal, CBS and ABC among other stops.
"Always a gentleman," Bloomberg founder and former New York City Mayor Michael Bloomberg said in a story on Prewitt's passing. "Ken will be greatly missed."
For a full obituary from Bloomberg, click here.