Medlock has led the company’s finance sector since 2004 and leaves the role to join a private, equity-owned business.
“I have been with Inmarsat for nine years and have hugely enjoyed my time at the company,” Medlock said in a statement.
“I leave the company both financially and operationally strong, at an extremely exciting time in its development. I am very confident that Inmarsat will continue to deliver value for shareholders and customers alike,” he added.
The board of directors is reportedly in the process of appointing a successor and Medlock will remain at the company until a suitable applicant is chosen, to ensure a smooth transition.
"Rick has been a valued member of the management team and has made a huge contribution to the success of the business. On behalf of the Board, I would like to thank him for his work over many years and wish him every success in the future," Andy Sukawaty, chairman at Inmarsat, said.
Inmarsat recently struck a deal with Telecom NZ for the management of its Global Xpress network.