Montgomery County Common Pleas Judge Mary Wiseman sentenced China Arnold, 31, of Dayton.
Arnold was convicted last week of aggravated murder by the same jury that recommended her punishment. Jurors deliberated about six hours on Thursday and Friday.
Prosecutors say Arnold intentionally put 28-day-old Paris Talley in a microwave and turned it on after a fight with her boyfriend.
The defence argued that someone else was likely responsible for the baby's death.
Medical experts testified that the baby died quickly after her temperature reached up to 42 Celsius. They said she probably was in the microwave for more than two minutes.
"She died because she was overheated," said Dr Marcella Fierro, retired chief medical examiner for Virginia. "She was cooked."
It was Arnold's third trial in her daughter's 2005 death. Her first trial ended in a mistrial. She was found guilty in the second, but an appeals court reversed the conviction.
Messages seeking comment were left today for the prosecutor and the defence attorney. A gag order has prevented anyone connected to the case from commenting outside court.
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