President Michael D Higgins signed the legislation this morning
Rent caps in Dublin and Cork - to limit the annual increases in rent - will come into effect tomorrow.
It comes after President Higgins signed the legislation today.
The Planning and Development (Housing) and Residential Tenancies Act 2016 takes legal effect immediately, but the clauses on rent caps in "rent pressure zones" take effect tomorrow.
The caps of 4% could be introduced to other cities and commuter areas from next month, after inquiries by the Residential Tenancies Board.
The legislation was passed in the Dáil last week after two days of often heated debates.