"This decision reflects the Administration's commitment to closing the detention facility at Guantanamo Bay," Psaki told reporters at her daily news conference.
Sloan would resume duty on July 1.
The continued operation of Guantanamo is not efficient, effective, or in the interests of US national security, Psaki said referring to a recent statement by President Barack Obama in this regard.
"Special Envoy Sloan brings a wealth of experience as an accomplished litigator and pragmatic problem-solver, skills that will prove valuable as he serves as lead negotiator for the transfer of Guantanamo detainees abroad and manages the multitude of related issues," she said.