Priest co-founded Adam & Eve with James Murphy, David Golding and Jon Forsyth in 2008. He will leave the agency in June.
Last year the founders completed their earnout from their sale to DDB in 2012 and Campaign estimated that they pocketed £110m altogether. The agency marked its tenth anniversary in January.
Priest has led celebrated work for brands such as John Lewis, including the retailer's classic Christmas ads "The long wait" and "Monty's Christmas" and brand campaign "Always a woman".
The agency’s creative work has led to seven Cannes Grand Prix, Agency of the Year at Cannes in 2014 and topping the Gunn Report in 2017. It has also been named Campaign’s Agency of the Year five times.
Priest told Campaign: "I really wanted us to win [Campaign's] Agency of the Year last year. We did that, then we had our tenth birthday and it started to feel like this was the moment to bow out.
"I really love this business but I want to do other things. I don't want to go and work for another agency, I don't want to sit in meetings talking about brand onions and laddering-up. I've had a great time in advertising, I've loved it very hard, but I'm done."
Murphy and Golding remain at the agency in group level roles, having handed the reins over to a new management team last year, made up of Richard Brim, Tammy Einav, Mat Goff and Alex Hesz.
Co-founder Forsyth left in 2017.