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When we are first introduced to Jarre in Blood of Elves, he is merely sixteen years old and studying to be a scribe at the Temple of Melitele in Ellander. He is one of the very few males at the temple, possibly the only one in residence. He is secretly in love with Ciri and has a crush on Triss Merigold.

The sixteen-year-old Jarre was the high priestess's ward, being prepared by her to be a cleric and chronicler. He lived in Ellander where he worked as a scribe at the municipal tribunal, but he spent more time in Melitele's sanctuary than in town, studying, copying and illuminating volumes in the Temple library for whole days and sometimes even evenings.
— pg(s). 266, Blood of Elves (UK edition)

Spoiler warning: Significant plot details follow.

Later in the saga, Jarre tries to join the Mahakam Volunteer Army but is ultimately assigned to the Poor Fucking Infantry, together with his childhood "friend" Melfi. The PFI, under the voivode Bronibor, takes part in the Battle of Brenna and is charged with stalling Nilfgaardian advance until reinforcments arrive. Consisting of commoner pikemen with little to none combat experience and matched against the enemy's heavy cavalry, the PFI sustains heavy casulties and Jarre loses his left hand in the battle. His unit successfully halts the enemy however.

Some time after the war, he settles down and marries a girl called Lucienne and writes a book called "Annales seu Cronicae Incliti Regni Temeriae" (which roughly translates to "Annals or Chronicles Celebrating Temerian Rule"). It's known that his granddaughter's name is Ciri.

Significant plot details end here.