Learn the essential steps on how to add a cosigner to a lease to strengthen your rental agreement. A guarantor or cosigner for an apartment could help you fill financial gaps when applying for your rental.Find which is right for you. You might need a cosigner if you're legally an adult, especially if you have no credit history, limited income, or no prior rental history. Com or ask your property manager about Leap. Your cosigner will typically be required to fill out and submit the same application you as the tenant have to submit prior to being approved. When you cosign an apartment lease, you give your legal guarantee that the rent on that apartment will be paid. As a co-signer, you don't have to live in the apartment but your name will be on the lease and you'll be legally obligated to follow the terms of the lease. If a potential renter has a low income, zero rental history or bad credit, the landlord might require them to have a co-signer on the apartment lease. The first step to taking on a cosigner is requesting they fill out an application, just like the tenant.