The three-judge panel of the appellate court voted 2-1 Wednesday to overturn the 2012 conviction, The Des Moines Register reported.
Meerdink, 31, of Scott County, killed his 7-month-old Boston terrier with a baseball bat in December 2011 after it had an accident on the floor and bit a child.
Chief Judge Larry Eisenhauer and Judge Mary Tabor, who voted to overturn the conviction, said prosecutors failed to prove Meerdink acted with sadistic intent to cause the death of the puppy -- requirements spelled out in the state's animal cruelty law.
They also noted Meerdink beat the dog only after trying other measures to control its behavior.
A spokeswoman for the Iowa attorney general's office said state lawyers had not yet decided whether to seek further review by the Iowa Supreme Court.
Meerdink, who was out on parole for a drug conviction when the incident occurred, was sent back to prison after the cruelty arrest. He was released on parole in April.