I am one of four roommates in my house, and we have no lease agreement. Myself and two of my roommates are in agreement, that the other roommate is disruptive to our environment. He continually gives his key out to friends and family, allows his girlfriend to park in spaces not designed for visitors (when we don't have space for everyone in the house to park) and his room smells like dead animal. My question is what is the proper way to ask this roommate to leave, and would I have to involve my landlord. I don't believe he will just leave and I need to be able to protect myself and my other roommates in the case that he will not leave quietly.

First question is there a lease between the landlord and someone?

But the bottomline here is that you will need to go through a formal eviction. The questions is whether the landlord needs to get involved or not. If this tenant does not have a lease with the landlord, the original tenants would be considered HIS landlord. If there is no written lease, then he's a month to month tenant and you would need to give him notice of one full rental period. If he doesn't vacate at that point you go to court for an eviction order.

You can start by asking the roommates to leave, if that don't work then you will have to start a formal eviction. This starts with a 5 days to leave, after that you will have to go to the court house. You might want to inform your landlord to what is going on.

I am one of four roommates in my house, and we have no lease agreement. Myself and two of my roommates are in agreement, that the other roommate is disruptive to our environment. He continually gives his key out to friends and family, allows his girlfriend to park in spaces not designed for visitors (when we don't have space for everyone in the house to park) and his room smells like dead animal. My question is what is the proper way to ask this roommate to leave, and would i have to involve my landlord. I don't believe he will just leave and i need to be able to protect myself and my other roommates in the case that he will not leave quietly.
There is no lease agreement between the landlord or any of us. We all moved in at the same time one year ago. The roommate in question pays his rent directly to our landlord. If we were to sign a lease now and exclude the disruptive roommate for our lease agreement would he then have to move out, or could that give us better grounds for eviction.

There is no lease agreement between the landlord or any of us. We all moved in at the same time one year ago. The roommate in question pays his rent directly to our landlord. If we were to sign a lease now and exclude the disruptive roommate for our lease agreement would he then have to move out, or could that give us better grounds for eviction.

The bold part is the key here. This means the agreement, even though unwritten is between the individual roomates and the landlord. In that case, only the landlord can evict him.

Yes, if you sing a new lease with the landlord excuding him, that would help, but only a little. The landlord would still have to inform him that he is terminating his tenancy, giving him appropriate notice. Then start eviction proceedings if he doesn't comply.

So by signing a new lease we make it the landlords problem, and because he pays him directly we have little to no options to make him leave. Are we allowed to tell him to move out and hope that he complies? My landlord would prefer to not get involved, but is willing to act as a mediator, is there any other options with out asking my landlord to evict?

Its already the landlord's problem because the tenant pays him directly. And yes, you can't evict him because of that. You could threaten to the landlord that you will all move out and he might decide that having three instead of one is better. You can also offer to pay any costs of eviction.