The core requirements sit in section 62(1) of the Residential Tenancies Act 2004. A valid notice is in writing, signed by the tenant, states the date of service, and specifies the termination date by day, month and year. It must also tell the landlord that any issue about the validity of the notice, or the tenant's right to serve it, has to be referred to the Residential Tenancies Board under Part 6 within the period set by section 80: 28 days where section 68 applies, 90 days in every other case. Leave that sentence out and the notice is defective.
Notice periods for an ordinary termination come from Table 2 to section 66. They run from 28 days for a tenancy of less than six months through 35, 42, 56 and 84 days, and reach 112 days once the tenancy has lasted eight years. Section 65 allows a longer period than the minimum, but caps it at 120 days for a tenancy under six months. Where the landlord has breached the tenancy obligations, section 68 reduces the notice to 28 days, provided the tenant first notified the landlord in writing and the failure was not remedied within a reasonable time, and to 7 days where the landlord's behaviour poses an imminent danger of death, serious injury or damage to the fabric of the building.
Fixed-term lettings follow section 58(3): they can be ended early only for breach, or where the agreement says otherwise, typically through a break clause. Section 186 adds an exit when the landlord refuses consent to an assignment or sub-letting (not available in student accommodation or certain approved housing body tenancies), and section 58(4) lets students in student-specific accommodation leave between 1 May and 1 October with 28 days' notice. The Board summarises these routes in its guidance on how a tenant can end a tenancy in Ireland.