Hick joins Fortescue at a time when the iron ore giant is delving into mining of critical minerals and rare-earths and is also striving to transition into a green energy firm through its unit Fortescue Future Industries (FFI).
Hick spent more than two decades at Woodside, most recently as the executive vice-president of Australian operations, part of the team that led the company through its $40 billion merger with global miner BHP Group's petroleum arm.
She will lead Fortescue Metals' mining arm, culminating a year-long search by the company's billionaire-founder and chairman Andrew Forrest.
Hicks will help the company "step beyond fossil fuels", said Forrest.
Gaines, who oversaw a tripling in the share price of one of the world's biggest iron ore miners in the past four years, remains on Fortescue's board as a non-executive director.
Last week, former Reserve Bank of Australia deputy governor Guy Debelle stepped down as the finance chief of FFI. Mark Hutchinson, a former president of General Electric's European operations, is slated to helm FFI by 2022-end.
(Reporting by Harshita Swaminathan and Savyata Mishra; Editing by Uttaresh.V and Sherry Jacob-Phillips)
