It is known that Chewbacca was a Wookiee that fought (along with other Wookiees) for the Republic during the Clone Wars, but is there any information on what he did before the Clone Wars and Episode III?
Like most topics regarding Star Wars after the canon shift, you have two different answers.
In terms of current Canon for Chewie, not a lot has been said as yet about his past history prior to the Clone Wars or in the period between Revenge of the Sith and Solo. However, we do have a paltry amount of information. Chewie was born some 180 years prior to the start of the Clone Wars, was married to Mallatobuck before the Rise of the Empire, and had a son, Lumpawaroo, in that time period as well.
In the Legends continuity, we have somewhat more information about Chewie's earlier life. For one thing, in the years prior to the Clone Wars, Chewie travelled throughout the Galaxy and eventually became a renowned hyperspace navigator among the Wookiees' Claatuvac Guild, an organization that worked with mapping and finding new and existing hyperspace routes. Chewbacca also met Obi-Wan Kenobi and Qui-Gon Jinn during a dispute over a Wookiee colony on the world of Alaris Prime in the Kashyyyk system, which Chewie helped lead against a Trade Federation incursion. He also courted his future wife Mallatobuck in his youth but they did not renew a romantic relationship until after the end of the Clone Wars.
I've only put in some of the highlights of Chewie's Legends life; there's a bit more information on Wookieepedia but the gist of it is all there.
The (horrible yet canonical) Star Wars Holiday Special shows Chewbacca has a home, wife, and kid. He was most likely just living the normal Wookiee life with work and family until the Separatists invaded. His piloting skills, weapons proficiency, being on the front lines during the Clone Wars, the sash he wears, and implied resistance to the Empire makes me guess he was a soldier in the Wookiee army, but I can't find any sources on that.