The restored Claude Monet painting 'Argenteuil Basin With A Single Sailboat' has been returned to the National Gallery and has gone on public view.
It was badly damaged two years ago when a museum-goer allegedly put his hand through the work.
The 1874 painting will be kept behind a protective glass case in a bid to prevent anyone getting too close.
It is valued at €10m and is one of only three Monet works in the State.
The other two are in the Hugh Lane Gallery in Dublin.
National Gallery director Sean Rainbird likened the meticulous repair to microscopic needlework.
"It was huge damage, shocking damage," he said.
"This project to restore and conserve one of the gallery's most popular impressionist works of art is testament to the outstanding expertise and dedication of our professional team of conservators," he added.
Exciting news, after 18 months of extensive conservation work Monet's 'Argenteuil Basin with a Single Sail Boat' goes back on display today.— Nat Gallery Ireland (@NGIreland) July 1, 2014
The oil painting is relatively small at 55cm by 65cm but regarded as a classic with its own significance.
It was painted at a time when Monet was using a boat as a floating studio on the Seine to paint scenes of the river and its banks.
He painted the scene in his own distinctive brushstroke style and contemporary colours in the same year that the first impressionist exhibition was held in Paris.
The painting was bequeathed to the State by dramatist and politician Edward Martyn who bought it on the advice of his cousin, the writer George Moore, who lived in Paris and knew the impressionists.
The repair work first involved gathering hundreds of microscopic fragments of paint which broke off the canvas in the vandalism - most measured 0.3-1mm across.
7% of the tiny pieces could not be saved after some split into powdery dust and were too tiny to reattach in the jigsaw restoration.
Conservationists revealed how they removed the painting from its frame and delicately sewed together thousands of fine threads which made up the canvass.
Under a microscope and using surgical tools and special heaters, they reattached fine materials with a specially formulated adhesive which has been used in similar work in Germany for the last 40 years.
The varnish, which covers the oil paint, was also cleaned before returning it to the gallery giving it a brighter and fresher feel, closer to what the original artwork looked like 140 years ago.
The canvass has been lined across the back to provide additional support to the repair work.
Simone Mancini, the gallery's head of conservation, said: "The National Gallery's approach to the conservation of Monet's painting was primarily dictated by the need to retain the integrity and originality of the painting and by applying the principles of reversibility, clarity and minimum intervention."
The restoration was supported by BNP Paribas.
The bank's funding allowed for the hiring of a Monet Paintings Conservation Fellow, Pearl O'Sullivan, specialist tools and materials, research and the publication of an online education resource on the gallery's French 19th collection.