The 1874 work, Argenteuil With A Single Sailboat, was ripped and perforated while on display in the millennium wing in what the institution described as an unfortunate incident on Jun 29.
Sean Rainbird, director of the National Gallery of Ireland, said the conservation will take about a year.
“Conservation work on the Monet is our primary concern given the extensivenature of the damage.
“The gallery’s conservation department will begin a thorough assessment of the work to be carried out in consultation with colleagues in sister institutions.
“We anticipate the process of conservation could take up to a year.”
Andrew Shannon, aged 47, from Willans Way, Ongar, Co Dublin, was charged with criminal damage to the painting. A court has been told he will deny the charge.
The gallery said that the Monet was under Garda control since the incident but has been handed back to allow urgent conservation to begin on Monday.
The work will be intricate and delicate. It is understood the first step will be to stabilise the painting to contain and eventually reduce the structural distortion of the canvas support.
Simone Mancini, head of conservation in the National Gallery of Ireland said: “Our theoretical and technical conservation approach will be dictated by retaining the integrity and originality of the painting.”