Twenty-five-year-old Brandon Bishop pleaded guilty Wednesday to aggravated assault for a series of assaults between March and May.
Police say the abuse was reported by a relative who noticed the girl was limping and missing clumps of hair. Officers who interviewed Bishop say he told them he beat the girl to make her tougher.
Matthew Falk, a Lehigh County prosecutor, says Bishop made no effort to hide the abuse from his wife.
The girl's mother, Candace Watts, pleaded guilty Wednesday to child endangerment and agreed to testify at Bishop's Jan. 25 sentencing.
The couple got married a few days before their arrests in June.