A US appeals court has thrown out the life sentence given to a teenager who was convicted of fatally shooting Australian baseball player Christopher Lane in 2013.

Chancey Luna was tried as an adult in the killing of the 22-year-old, who was shot while jogging along a road in the small town of Duncan in Oklahoma.

During the trial, prosecutors said Luna, Michael Jones and James Edwards Junior, decided to kill someone "for the fun of it".

Their lawyers denied that, admitting Luna fired the shot but saying it was not intended to kill.

Luna was 16 at the time of the shooting and was convicted of first-degree murder and sentenced to life in prison without parole.

Chancey Luna was 16 when he was arrested and charged with Chris Lane's murder. ( Reuters )

In a court filing, Luna's attorney argued that life-without-parole was an unconstitutional sentence for a juvenile, and the Oklahoma Court of Criminal Appeals agreed.

It has upheld his conviction and ordered a resentencing.

Lane was on a baseball scholarship at East Central University and was two weeks away from celebrating his 23rd birthday when he died.

He had only been back in the US for two days after a trip to Australia with his American girlfriend, Sarah Harper.