A "unique and beautiful" £2 million collection of art is to be donated to Glasgow.

The 15 works by the French artist Niki de Saint Phalle, the most significant bequest to the city's galleries in recent years, are being donated to the city by Eric and Jean Cass, business people who have collected art for more than 30 years and are now dispersing their collection through the Contemporary Art Society.

The works, including sculptures, a print, wallpaper and rare archive material, will make it the largest collection of the French artist's work held in the UK, and will be shown at an exhibition planned for the Gallery of Modern Art (GoMA) in 2013.

The gift, presented by the Contemporary Art Society, adds to the two sculptures and two installations by Niki de Saint Phalle Glasgow already owns.

The collection of 15 works is understood to be worth around £2m.

De Saint Phalle was born in 1930 in France and died in 2002.

She began producing her first paintings in 1950, and this led to plaster works and her "shooting paintings" – these pictures were made of plaster, with containers of paint beneath the surface, which would explode when she shot them.

In 1965, she created her first "Nana" – these large and brightly painted female figures were made originally in papier mache and later in polyester.

She also designed stage sets and costumes, created movies, graphic work, chairs and a sculptural playground.

In 1988, de Saint Phalle helped to design the iconic Stravinsky Fountain at the Pompidou Centre in Paris.

Councillor Gordon Matheson, the leader of Glasgow City Council, said: "This extraordinary and generous donation is unprecedented for GoMA so it's hard to properly express just how grateful we are.

"The support from the Contemporary Art Society coupled with the incredible generosity of Eric and Jean Cass has allowed us to once again grow Glasgow's collection of international modern art.

"These works are unique and beautiful and will captivate and thrill our visitors to GoMA when they are displayed in the autumn of 2013."

Eric and Jean Cass, who live in England, were unavailable for comment. However, they have dedicated more than 35 years of their lives to collecting and supporting artists, building a collection of more than 300 sculptures, ceramics, drawings prints and paintings including work by artists including Barbara Hepworth and Henry Moore.

Paul Hobson, the director of the Contemporary Art Society, said: "We are delighted to be able to make this gift to Glasgow Museums.

"Working with Eric and Jean Cass and learning more about the collection that they have so carefully developed over the years has been inspirational.

"The Contemporary Art Society has a unique view of public collections across the UK and this gift is one of many initiatives that we are championing in museums across the UK.

"We look forward to seeing the works displayed within the collection at the Gallery of Modern Art and hope that audiences will enjoy this exceptional group of works for years to come."

Glasgow's contemporary art scene has been highlighted in UK and international news in recent weeks, following the success of Martin Boyce, a Glasgow-based sculptor, in winning the Turner Prize, the most prestigious award in contemporary art.

Boyce scooped the £25,000 award, following in the footsteps of fellow Glasgow artists Susan Philipsz and Richard Wright.

Founded in 1910, the Contemporary Art Society exists to support and develop public collections of art in the UK.

It raises funds to purchase and commission new works for a network of public collections, which subscribe to it as Member Museums and Galleries, and by soliciting gifts of works to these collections for public benefit.