China Arnold was sentenced in 2008 to life in prison without parole after being convicted of killing 28-day-old Paris Talley in August 2005.
The conviction was reversed by the 2nd District Ohio Court of Appeals based on prosecutorial misconduct and a witness's recanting of her testimony, said Arnold's attorney, Jon Paul Rion.
"We are very thrilled about the results," Rion said. "We realized from the first day she was innocent and we have maintained that."
Montgomery County prosecutors are reviewing the ruling before commenting, prosecutor's spokesman Greg Flannagan said.
Arnold was sentenced following her second trial. The first ended in a mistrial.