It follows the announcement in December that current CEO Elizabeth Gaines would step down.
At the time, global executive search firm Egon Zehnder was appointed to "identify a CEO and other leaders with exceptional skills and global experience across heavy industry, manufacturing, and renewable energy".
Today it was announced founder and non-executive chairman Dr Andrew Forrest AO would become executive chairman.
Forrest was in Papua New Guinea recently in an effort to establish hydroelectric power stations under the banner of group company, Fortescue Future Industries.
The company said Forrest would specifically oversee the iron ore business "for an interim period" when Gaines stepped down in August.
It is unclear how long the interim period will be or who will run the iron ore business beyond that time, but it is understood the search for a CEO continues.
Forrest founded FMG in 2003 and ran it until mid-2011, when he transitioned to non-executive chairman and Nev Power took over as CEO.
While Forrest stepped back to focus on his philanthropic causes through family office Tattarang, he had already been devoting most of his time to FMG in the past couple of years since the launch of green arm FFI.
Forrest and his wife Nicola are FMG's largest shareholder with more than 30%.
FMG also appointed former GE Europe CEO Dr Mark Hutchison as CEO of FFI.
Hutchison, who will be based in Perth, will join FFI in early July, initially as director of projects, and become CEO by the end of the year, reporting directly to the board.
Current FFI CEO and FMG deputy CEO Julie Shuttleworth will continue as CEO before moving to a senior position with FFI.
Hutchinson said joining FFI was the opportunity of his lifetime.
"We must urgently reduce emissions now and at scale," he said.
"No longer should the world be dependent on heavily polluting fossil fuels. The green industrial revolution is well underway globally and Fortescue is leading it. As a result of this revolution, we will see an explosion in manufacturing and green energy jobs worldwide with great benefits for local communities."
Former AGL Energy CEO Andrew Vesey has been appointed as head of energy transition projects at FFI, while founder of McKinsey & Co's Perth business Christiaan Heyning has been appointed as head of decarbonisation.
FFI's current director of projects Gordon Cowe will become head of projects evelopment.
They will join recently appointed FFI chief financial officer, former Reserve Bank of Australia deputy governor Dr Guy Debelle, who starts next month.
FMG has appointed BlackRock China director Li Yifei to its board. With Gaines staying on as a non-executive director (as well as FFI global brand ambassador), FMG's board will be majority female.
Other new appointments included deputy FMG chair Mark Barnaba and former tech CEO Dr Jalal Bahherli as co-chairs of newly acquired subsidiary Williams Advanced Engineering.
Forrest said the company was committed to "sharply arresting" climate change, creating economic growth and jobs and growing the business.
"We will prove that going green has a fabulous and profitable future, providing significant additional value for shareholders by ramping up innovative and game changing green technologies, green operating know-how and sharing that and our future massive green fuel supply to the world," he said.
"Today is a further progression of Fortescue's transition to a global, green renewable and resources company. This growth and value to shareholders is already evident with our shareholder base doubling since FFI was launched, with our investors ranging from top tier institutional banks to grassroots investors, all wanting to be a part of this mission, as we continue to strongly outperform our peers in the iron ore sector.
"We are doing the hard work to genuinely decarbonise Fortescue, avoiding the temptation we see all around us to greenwash.
"I wish to specifically congratulate Rio Tinto and BHP for their efforts in their own inevitable decarbonisation journey. For those remaining in the private and public mining and energy sector who ignore the world's need to change, you do so at your ignorance and peril."
FMG shares were trading 0.5% to $A19.50, valuing the company at around $60 billion.