The bank had already announced that Lucas-Bull intended to depart at the end of her current term, when she will leave to head the board at retailer Shoprite.
Moloko has spent three decades in the financial services industry, including as a former chief executive of insurer Old Mutual's asset management business.
He has also served as chairman of the board for asset manager Alexander Forbes and miner Sibanye-Stillwater.
(Reporting by Emma Rumney; Editing by David Goodman)
