Even if you meet income requirements, if they run your credit and it's low, they will often require a co-signer as risk mitigation. Learn the essential steps on how to add a cosigner to a lease to strengthen your rental agreement.Com or ask your property manager about Leap. A guarantor or cosigner for an apartment could help you fill financial gaps when applying for your rental. Find which is right for you. All members of a signed lease, including a cosigner, need to sign a lease addendum for the addendum to be valid? We will act as your co-signer to help you qualify for an apartment or rental home. For applicants with no credit history, a cosigner may be considered. Any "ground rules" are totally unenforceable. They sign their name to the lease agreement and are held fully responsible for rent if the tenant stops paying rent.