Kirby, whose first day on the job was today, will be responsible for explaining US foreign policy to the world, a role that makes the post of State Department spokesman one of the most visible in government.
Kerry praised Kirby for his "impeccable judgment, collegiality and character" over the course of a military career that culminated as the top Defense Department spokesman.
"All of this makes him the perfect person to help tell America's story to the world," Kerry said.
Kirby was the Pentagon's press secretary from December 2013 until February, stepping down after new Defense Secretary Ashton Carter said he wanted a civilian in the job.
Kerry also praised the work of acting State Department spokeswoman Marie Harf, citing her role in devising the agency's communications strategy on the nuclear negotiations with Iran.
Both Harf and Psaki were frequent targets on social media, especially Russian media, which they attributed to sexism.