Economidis held the VP operations role since 2018 and was instrumental in the company's return to a strong operating performance.
South32 CEO Graham Kerr said Economidis was an experienced mining executive having worked in the mining sector in Australia for more than 25 years running large-scale operations with companies including Orica, Peabody, Vale and BHP.
"Jason brings a wealth of knowledge and experience to our Australian operations and I congratulate him on this new position," Kerr said.
Bull, who has worked in the resources industry for more than 40 years, was most recently general manager of the Appin mine in New South Wales, where he helped get that mine back to strong operating performance.
"It's an absolute honour to lead the very talented and hard-working team at South32 Illawarra Metallurgical Coal," Bull said.
"I am very proud of the work we do and of our place in the heart of the Illawarra community."
Bull began his career in the UK before moving to Australia in the 1990s and working in senior leadership roles, including a period as development manager at Dendrobium mine under BHP's ownership.
Bull joined South32 Illawarra Metallurgical Coal in 2017 and previously worked as general manager Dendrobium mine, where he helped restructure mine and coal preparation plant operations and improved health and safety.
He then took on his role at the Appin mine.