A guarantor is a person or a company who will co-sign on your lease in case you do not qualify to rent an apartment in New York on your own. So I would recommend setting your guarantor approval up first before applying to an apartment.Com or ask your property manager about Leap. While tenants in rent regulated or government subsidized apartments have special rights, many rules and laws apply to both unregulated and regulated apartments. In addition to this rental application, you will also be required to provide a copy of a valid form of identification and proof of income. A guarantor must complete a rental application and pay the application fee. A guarantor is a person who also signs the lease as a third party, but they aren't entitled to live on or have access to the unit. In simplest terms, a guarantor is a tenant who does not live in the apartment. 1. Assemble all the required materials. Before you begin filling out the guarantor form, make sure that you have all pertinent materials.