30-year-old, Birmingham-born Osbourne, who is a product of Aston Villa's youth system, returns to the club just over a year after refusing to play under then-manager Jon Whitney, after a falling out between the pair.
Along with Aston Villa and Walsall Isaiah has also chalked up appearances for Nottingham Forest (loan), Middlesbrough (loan), Sheffield Wednesday (loan), Hibernian, Blackpool, Scunthorpe United, and Forest green Rovers, who he joined after leaving the Saddlers at the end of the 2016/17 campaign.
Speaking via the club's official website - Saddlers.co.uk - Isaiah said; "I am happy to be back here. When I was here last time, I connected well with the fans and hopefully that can happen again. I was happy to hear what the manager had to say about how he wants to play football. The way he spoke made me think this was the best place for me.
"There were a lot of key factors in me coming back here. A big part was being able to bring my family to games. Being around my kids helps because I have four of them and I wanted to be around them more. Not only will I be looking to guide players, I think the players will be looking to me for advice as well. I will try and help the young players through games and make sure they progress because I am sure they all want to play to their full potential."