John's voice resembled that of Harry and he wasn't dissimilar to him physically.

[alpacinou]

I want to say a person resembles another person. Can I use "dissimilar"? Is this correct?

John's voice resembled that of Harry and he wasn't dissimilar to him physically.

 

[Skrej]

You could, but it's not very natural. Even so, it needs a comma before 'and'.

The only reason to do so would be a deliberate attempt at humor or irony.

 

[tedmc]

I don't like the use of a double negative along with a positive.

John's voice resembled that of Harry and they are quite similar physically.

 

[Barque]

I don't think "resembled" goes with "voice". It suits looks, not sounds.
"Similar/dissimilar physically" doesn't sound very good to me either. It sounds as if you're referring to build rather than features or overall appearance.

John's voice was like Harry's, and they looked like each other too.
John's voice was like Harry's, and they resembled each other too.
John's voice sounded like Harry's, and they were similar in appearance too/weren't dissimilar in appearance either.