He was arrested, tried, and sentenced to 20 years with hard labour. This was the maximum sentence the courts could give him, since he was under 20 years old. Of the other assassins and other people involved, some received death sentences and were executed, some received death sentences and had their sentences commuted, and some were sentences to different terms of imprisonment. Some of those arrested were acquitted.

Princip died of tuberculosis in prison in 1918; he already had the disease when he took part in the assassination.

More detail here: https://www.reddit.com/r/AskHistorians/comments/d30nlw/why_wasnt_gavrilo_princip_executed_following_his/