Twenty-eight-year-old Keith Bulloch is charged with murder by abuse or neglect in the first degree and resisting arrest.
Investigators say last summer someone called 911 from a home on Palace Avenue in Claymont when they found the little girl unconscious and unresponsive.
An autopsy determined the cause of death was fentanyl and cocaine toxicity.
On Tuesday, detectives obtained a warrant for Bullock and took him into custody.
He is behind bars on $1 million bail.