Will I be breaking any laws by changing the locks and putting all of my roommate's possessions on the porch?

Dear Morgan:  Generally speaking, the law requires that the landlord go through the proper legal channels to evict someone from the property.  The law does not permit a co-tenant to evict another co-tenant.  Since you both share a lease, you are co-tenants.  If the other tenant was sub-leasing form you, that would be different.  But since you share the lease, you both have the same legal rights to the premises. If you do perform any of the above, your co-tenant could potentially sue you for damages, including any damage to his belongings, moving expenses, living expenses until he finds a new place to live, etc.  He could also contact the police and file a complaint against you. If he is breaching the terms of the lease, then you need to inform your landlord and demand that they formally evict him from the premises.  If he is breaching the agreement with the landlord that he would move out by a certain date, then he is potentially a holdover tenant, and the law provides the means for a landlord to evict him.  But it is up to the landlord to do this, not you.  If you assist the landlord with an improper/illegal eviction (i.e., move his stuff out, change the locks, etc. without a proper court order) you could be held equally as liable as the landlord. You pay rent to the landlord to protect you against this stuff.  Make the rental company do their job and evict him properly and legally. Best of luck to you.