Kelly, 48, was hired by the NFA board of trustees in May after the departure of Head of School David Klein.
He attended virtual meetings, had NFA staff drop off any documents he had to sign, and finally arrived on campus Tuesday.
Freshmen and students at the NFA Sachem Campus are scheduled to start Aug. 26 and grades 10-12 on Aug. 27.
Kelly hopes to keep NFA as an attractive school for foreign families looking to educate their children in the United States.
“Shifting from international education to NFA isn’t that much of a stretch because of the diversity that’s here.