This will result in the Hilton Dublin hotel having a total of 305 bedrooms.
Mr Malone, reputed to be the largest landowner in the US, bought the hotel for around €30m in 2014.
He also owns the five-star Intercontinental hotel in Ballsbridge, and the five-star Westin hotel in College Green, while he recently added the Spencer, Morgan and Beacon hotels to his growing Irish portfolio.
His stock market-listed Liberty Global media giant owns TV3 and Virgin Media.
An Bord Pleanála said the proposed development would not seriously impact either the visual or residential amenities of the area, nor have an adverse impact on the character or setting of the Grand Canal Conservation Area.
Dublin City Council gave the plan the go-ahead earlier this year but it went before An Bord Pleanála after appeals were lodged against the decision.
The expansion will go some way towards easing the demand for hotel rooms in the capital.
A recent report from the Irish Tourist Industry Confederation estimated there was a need for 30 more hotels providing 5,000 additional rooms in the next few years.
In a written Dáil reply on the issue, Minister of State for Tourism and Sport, Patrick O’Donovan, said the bulk of the new room stock will not come on stream until after 2018.