Dan Riccio, Apple's vice president of the hardware engineering team for the iPad, will replace him.
The transition will take "several months," the company said.
It's unusual for Apple to see turnover in its executive team, but it does happen. Mansfield was in charge of hardware engineering for the Mac since 2005, and for the iPhone and iPod since 2010. He was previously head of engineering at Raycer Graphics, which Apple acquired in 1999.
His replacement comes from a product design background, and has been at Apple since 1998.
It's possible to read into the switch as a way of indicating how the iPad is the future of hardware at Apple, but the truth is that the company's devices are growing increasingly similar from a hardware perspective. It may be more interesting to see where Riccio takes things from here as the new steward of the group.
"Dan has been one of Bob’s key lieutenants for a very long time and is very well respected within Apple and by the industry," Apple chief executive Tim Cook said. "Our hardware engineering team is the best engineering team on earth and will not miss a beat during the transition."