The cause of death has not yet been released. Haines joined CNBC in 1989. Mediaite:

CNBC anchor Mark Haines has died, the network said Wednesday morning. CNBC president Mark Hoffman called Haines a “building block” of the financial networks’ programming.
“With his searing wit, profound insight and piercing interview style, he was a constant and trusted presence in business news for more than 20 years,” Hoffman said in a statement to CNBC employees. “From the dotcom bubble to the tragic events of 9/11 to the depths of the financial crisis, Mark was always the unflappable pro.,” said Hoffman. “Mark loved CNBC and we loved him back. He will be deeply missed.”
The New York Stock Exchange paused for a moment Wednesday in honor of Haines.