Grivner is an industry veteran with 25 years of leadership experience, spending 12 of those as CEO at several telcos.
Before Colt, he served three years in Singapore as CEO of Pacnet and held several executive roles such as at Cable and Wireless, Ameritech, and IBM.
Grivner was CEO of Colt when he joined the board of directors at GCX back in April.
Jim Ousley, Chairman of GCX, said: "We are very pleased to have someone of Carl's caliber and experience to lead GCX.
"It was a great experience working together at Pacnet, and I am looking forward to the opportunity to work together again - along with our entire senior leadership team - to strategically lead and drive GCX's next phase of growth and market leadership."
Grivner added: "It is an exciting time to get back into submarine networks, as the demand for global bandwidth is multiplying, and there is an increasing need for fiber optic interconnectivity to support the rising global data traffic.
"GCX is in a unique position to support the escalating bandwidth consumption across emerging markets as it owns and operates one of the world's largest private submarine cable systems, which sets the foundation for a robust global service delivery platform.
"I am thrilled to join the GCX team. Together, we will capture the next waves of growth for GCX by remaining laser-focused on serving our customers, refreshing our technologies and solutions, while creating significant value for our shareholders."