I recently found out that my apartment is an illegal conversion and have been moving out because of it. It's been very inconvenient and difficult on short notice. I have a new place and am paying rent there, and moving my things out of the old apartment. I stopped paying rent at the old place and my landlord is trying to collect it from me even though he's been issued violation notices from the dept of buildings, and I don't even live there anymore. What should I do?

Get all of your old things out quickly before you can't.
Inform him that he is not able to collect rent from a illegal apartment. If he sues you in court, you will have to prove that he can not legally rent the apartment

Why do you think it is an illegal apartment? What about it is illegal? Depending on what makes it illegal could affect your ability to break the lease. Also how you went about breaking the lease matters too. Finally ANY question on law needs to include your general locale as laws vary by area.

If you find that the place you were living at was illegal, you can get your money back from the pasts months.

If you find that the place you were living at was illegal, you can get your money back from the pasts months.

Can you provide the location and laws to back that up? In my experience, even if the rental was not legal, the tenant still got value for their rent payments and that is generally not recoverable.

While it may not be legal for a landlord to rent a unit or property, generally, the penalty to the landlord is fines. The tenant may be forced to move, but will not recover rent paid.

ILLEGAL DWELLINGS
State Law says that it is illegal for a landlord to rent out an illegal,
Unpermitted or unapproved dwelling.  Some examples:

--  illegally converted garage,
--  illegal additional unit built without permits
--  illegally rented guest house
--  excessive boarders in an owner occupied home
--  illegally added room

When renting an illegal unit, the tenant may legally not owe any rent and actually be able to claim and receive a refund of part or all the rent they paid to live there!  At The Tenants Legal Center we have been successful in obtaining rent refunds for our clients who lived in illegal units.
What state do you live in?

ILLEGAL DWELLINGS
State Law says that it is illegal for a landlord to rent out an illegal,
unpermitted or unapproved dwelling.

Thank you, but what state is that from? Also, if you copy and paste from a WEB site, you need include a link to that site so it can be verified.

I live in the state of California. I was not aware I had to paste the link. However, I will include it below. I have gone thorugh an eviction and a lawyer told me I would loose. I stood by my I info. And sure enough I won. I will look for the civil code, but what state should I search for?
http://www.caltenantlaw.com/Habitability.htm

Scott I have seen this same thing in several states, GA, TN also has similar rules

I was not aware I had to paste the link.

I understand you didn't know, but we want to make sure of the accuracy of the advice given. I appreciate your providing the info. The OP (original poster) has not specified where they live so we don't know what laws to apply. I know in NY and several other states I've checked, a lot depends on the nature of the illegality. I've seen cases where homeowners rented an accessory apartment in violation of zoning laws where the tenants were not allowed to recover rental since they received value for it. I've also seen cases where the landlord was renting substandard accommodations and the tenant was awarded refund of rentals. However, they never collected since the landlords protected themselves.

So to scratch, you neglected to tell us where you are, or what the violations are so we don't know what the landlord's chances of compelling you to pay. You might try asking the dept of buildings.