Terence Darrell Kelly, 37, pleaded guilty last year to one count of forcibly taking a child under 16.
He will be sentenced in the WA District Court on Wednesday and could face up to 20 years' imprisonment.
Cleo was reported missing on October 16, 2021. She had been staying with her family at the remote Blowholes campsite, about 960km north of Perth.
Her mother Ellie Smith awoke in the early morning to find Cleo missing from the family tent, sparking a major police investigation.
The WA government announced a $1 million reward for information leading to Cleo's location or to the arrest and conviction of people involved in her disappearance.
Cleo was found by police on November 3 alone in a room at a property in nearby Carnarvon, 18 days after she was reported missing.
The dramatic rescue and Cleo's confirmation of her name was captured by an officer's body-worn camera and subsequently made news headlines around the world.
Kelly was taken into custody on the same day and later charged.
Earlier this year, he was fined after admitting to obstructing police officers at a regional station in the aftermath of his arrest.
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