Can you narrow it down a bit, time and culture wise?

Certainly in the Middle Ages there are numerous works of history written by people actively involved in warfare, alongside tons of works written by non-combatants.

Are there specific issues or questions you have on this subject?

What do you define as a "soldier"? Do officers and generals count?

Julius Caesar wrote 2 books and had military service both at lower levels (earlier in his career) and obviously as proconsul. Ammianus Marcellinus and Procopius both wrote histories of their eras and both served on the staff of active generals. Polybius had military experience and wrote his history of Rome and the Punic wars.

What you're unlikely to find is an ancient account from a regular, ordinary soldier. They didn't have the education or the resources to write something. Plus if they did, it would have to be deemed worthy of preservation and copied repeatedly over the generations until the age of the printing press. If only one generation thought that a soldier's writing wasn't worth the effort of copying it out (by hand) then it'd be lost forever.

An interesting note is that one of the books considered part of Caesar's "The Civil War". These (the African War, the Spanish War, the Alexandrian War) were written after Caesar's assassination by his officers. They obviously aren't at the same high level of writing that Caesar put out and the African War has been suggested to be the work of a grizzled old centurion (who most likely was from the lower upper class of equites).