The officer, Derek Carlile, was originally charged with second-degree manslaughter in connection with the fatal shooting, but the jury could not reach a unanimous verdict and a mistrial was declared. Prosecutors later dropped charges against Carlile.
In a brief statement issued Monday, Marysville city officials said Carlile was no longer employed by the police force.
"As a result of the findings of a police department internal affairs investigation, Derek Carlile's employment with the city of Marysville has been terminated, effective immediately," the statement said.
"Because the nature of this release regards a personnel matter, no further comment by the city of Marysville will be made."
Carlile's daughter, 7-year-old Jenna Carlile, was killed in the family's van on March 10, 2012.
Investigators said Carlile was off duty and headed to a wedding with his wife and children when they stopped at an art studio in Stanwood. Carlile and his wife left the children in the family van while they dropped off business cards. Carlile's loaded personal handgun was also in the van.
His 3-year-old son grabbed the weapon and unintentionally shot and killed Jenna, officials said.
Prosecutors argued that as a trained police officer, Carlile should have known the risks of allowing kids to be unsupervised around the gun, especially because his young son seemed fascinated with firearms. They said the child died because of Carlile's carelessness.
Carlile's attorney called the shooting a tragic mistake, not a crime.