Miller will replace Natascha Viljoen, who is leaving for gold miner Newmont Corp, as CEO from 1 October.
Miller has been finance director since 2019 and takes the helm after the company reported on Monday a 71% slump in first-half profit, hit by weaker platinum group metal prices, poor metal grades, rising costs due to high inflation and challenges at its flagship Mogalakwena mine.
"We must remain agile, adapting to market realities while focusing on efficiency and prudent resource management," Miller said in a statement.
Amplats shares have fallen 36% this year. The Johannesburg-based miner and its peers are battling debilitating power outages that are threatening growth.
Miller, a chartered accountant, is an insider at Anglo American, having also worked in the base metals and bulk commodities businesses at the group.
Still, he faces the challenge of finding solutions to expand Amplats' giant open-pit Mogalakwena mine, where the company has been exploring options to start digging for the metals underground.
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