This can actually be done, and how well the cat responds probably depends a lot on the nature of your cat.
If you have a cat that just loves attention, and follows you around already, then they will probably be fairly easy to train. However, if you have one of those more stand-offish kinds of cats that only like attention when HE wants attention, then he would be more likely to resent having a harness and leash put on him.
When I was a young girl, I had a favorite cat, and she was one of the kind that you can dress in doll clothes, or do just about anything with, and she enjoyed it.
First, I put the harness on her and let her get used to wearing that. Then I would call her to follow me along; so she got used to wearing the harness and following me.
When I first put the leash on the harness, she didn't know what was going on; but I called her and she just followed me, like always.
After walking around the yard with her for several days, she got the idea that she should follow me around with the leash, and she was fine with having the harness on.
I could then take her outside of the yard, and she would come along on the leash just like a dog would do.
