"I've had the privilege of spending 29 years doing something I love — how often does that happen?" Hart, 59, said in a statement. "I only meant to be at ET for three years, suddenly it's almost 30! I've reached a point when I clearly realize it's time for a change. There are many things I want to do in my life and I'd better get on with them."
Hart, a 1999 Broadcasting & Cable Hall of Fame inductee, joined ET in 1982.
"It will certainly be with mixed sentiments that I say 'goodbye' at the end of the season, but it will definitely be with a sense of celebration ... 30 years of Entertainment Tonight, are you kidding me? That's an accomplishment and something I'm very proud of," said Hart.
CBS said no decision has been made on Hart's replacement. Variety, however, reports that The Insider's Lara Spencer is in the running.
ET kicks off its 30th season on Sept. 13.
Who would you like to see fill Hart's shoes?