Construction of the tower is to begin imminently and the group is already in discussions with potential tenants, it is understood.
The long-running saga to build the 22-storey tower on Tara Street involved four separate attempts by the developer to secure permission. An Bord Pleanala approved the plans for the 88-metre structure last Friday.
The building will comprise 16,557 sq m of office and hotel accommodation and will be capable of accommodating 890 office workers, a 106-bedroom hotel over four storeys and a top-floor restaurant.
Ronan Group's senior development manager, James Ronan, said he was "thrilled" the development had finally been given the green light.
"This is an extremely positive and progressive move for Dublin and Ireland Inc," he said.
"If we are to continue to compete with our European counterparts for much sought-after foreign direct investment we need to set our ambitions high, delivering the world-class accommodation required to facilitate our collective growth ambitions."
Ronan said the development will be a "catalyst for the regeneration of this city quarter and will set a new benchmark for regeneration projects in the city".
Chairman of Henry J Lyons Architects Paul O'Brien said the project will have a "transformative regenerating effect on the Tara Street streetscape".
Despite repeated rejections to his plans, Johnny Ronan had secured the support of the Dublin Chamber, the Irish Hotels Federation, IDA Ireland and the Convention Centre Dublin.
The planning documents state that the tower will take 30 months to construct with between 313 and 375 workers employed.
Based on a previous planning application, Dublin City Council said the building would "seriously detract" from the character of Custom House, which it called "one of the city's most important architectural set-pieces".