Police officers found Leona Peach, from Newton Abbot in Devon, when they searched an address near Boston, Lincolnshire.
The 34-year-old man under arrest was due to be transferred into police custody for questioning in due course, Devon and Cornwall Police said.
“Following an extensive policing operation, 12-year-old Leona Peach, who was reported missing from Newton Abbot on the morning of Monday 20 December, has been located safe and well,” the force said.
“Aided by officers from Lincolnshire Police and with support from Devon child services and Lincolnshire child services, units attended and undertook a search of an address near Boston this afternoon and located Leona; she will continue to be supported by specialist officers and child services.
“During the search, police have arrested a 34-year-old man, originally from Devon, on suspicion of child abduction and kidnap.”
Police thanked the public for their support in helping find the girl.
During the search, they had issued an appeal to Leona or her father to contact them.