Harvey, like Kelly from Northern Ireland, spent 20 years playing the game and he was a boss for almost as long on the non-league scene.
Latics have said Harvey will also have “additional responsibilities in the areas of talent identification and scouting” while Kelly and his assistant Dean Holden, both 37, will also be able to lean on the 57-year-old’s experience.
“I will be doing anything that needs to be done,” Harvey told the club’s official website.
“With Darren being young and just coming into the job, and with Dean also being young, I’ll balance out the bit of inexperience.
“I’ve been in football for over 40 years and I have a lot of contacts and friends so I’m here to help and guide as much as I can to add my experience to the team.
“I’m really looking forward to getting involved and I’ve just been watching some DVDs from last season. I’ve been chatting with Darren and it’s getting me tingling again so I’m looking forward to the challenge.”
Kelly added: “Jim is going to work closely with me, Dean and the staff. I hold Jim in the highest regard. He is experienced in the game and I had the pleasure of working with him and I know what he’s about.
“For me personally, he is one of the best in the business. This is a massive signing for the football club because you’ve got to have the right staff behind you. I’m excited about working with him again.”