Edwin Alexander Andrade-Ramos, 27, was arrested by Arlington police on Wednesday and faces a charge of injury to a child/serious bodily injury.
Police said the child suffered multiple fractures on her body and a serious head injury.
The child's mom said when she arrived home from work on Jan. 28, she noticed her daughter, Marjorie Ramos-Pena, wasn't eating and was acting differently. The child eventually became unconscious and was rushed via ambulance to a local hospital.
The baby was treated, but died from the injuries Wednesday – the same day Arlington police arrested Andrade-Ramos for an August assault on the baby's mother, who is his common-law wife.
He later earned the charge of serious bodily injury to a child.
The mother works overnights at a nearby Walmart and would often leave Marjorie and her two other children in the care of Andrade-Ramos. The same was true on Jan. 28.
Andrade-Ramos remains in custody at the Arlington City Jail.