A masterpiece by French impressionist Paul Cezanne has been bought for a record $A16.2 million ($NZ19.52 million) by the Art Gallery of NSW, in its most ambitious purchase ever.

Bords de la Marne, painted by Cezanne in 1888, was in the private collection of a Swiss family for more than 100 years, before gallery curator Edmund Capon pounced to acquire a painting he admitted he had wanted for 25 years.

Capon said today the painting, the most expensive ever bought in Australia, was a major achievement for the gallery and the "most ambitious acquisition" in its history.

"Twenty-five years ago when we launched the (Art Gallery) Foundation, I put at the top of the list of things we needed to do was Cezanne," he said at the painting's unveiling in Sydney today.

"It's long overdue that we had one on the walls of this gallery."

The painting will be on public display in the gallery's old courts.