My dad has agreed to cosign a lease with me but I am afraid my application will just be thrown out since I cannot provide a credit score or any proof of income. A cosigner for an apartment takes on the financial responsibility for a lease.Learn how having a cosigner can help someone get approved for an apartment. When do I need a cosigner? So, in the event you do not qualify on your own, your landlord may ask you to get a cosigner or a guarantor to complete the rental application. Adding a cosigner to your standard lease agreement isn't difficult. Rather than writing a new lease entirely, you can simply add an addendum.