Mark Bridger has been charged with the murder and abduction of missing five-year-old April Jones.
The announcement was made ahead of a news conference led by Dyfed Powys Police and the Crown Prosecution Service in Aberystwyth.
Bridger, 46, has also been charged with perverting the course of justice.
The former lifeguard will be held in custody until he appears in court at Aberystwyth Justice Centre on Monday.
Iwan Jenkins of the Crown Prosecution Service said: "Having carried out a detailed review of the evidence gathered so far by Dyfed Powys Police I have come to the conclusion there is sufficient evidence to charge Mark Bridger with murder and it is in the public interest to do so."
The decision came just an hour before detectives reached the maximum 96 hours that they could hold Bridger before charging or releasing him.
Searches are still continuing in and around the town of Machynlleth in mid Wales for the missing girl.
The primary school pupil was reported missing on Monday evening after she was seen getting into a vehicle near her home at around 7.30pm.
Ever since, the community has rallied behind the efforts to find the youngster, many insisting that until she is found they still hold out hope of April still being alive.
Wearing a pink ribbon that has come to symbolise the search, the Chief Constable of Dyfed-Powys Police, Jackie Roberts, said: "Today our thoughts are very much with April's family, friends and those that knew her."
She added: "To see so many people give up their free time was truly humbling to all those involved.
"It is time to let judicial process take its course and time to let the family come to terms with what has happened over the past week."
Superintendent Ian John said 10 specialist police teams were deployed on Saturday morning to continue looking for April.
He added: "Despite today's announcement we are maintaining the momentum of the search and we remain totally focused and committed to finding April."