Born in Britain, Louise Vava Lucia Henriette de la Falaise was the daughterof an Irish mother, Maxime Birley, who modelled for Elsa Schiaparelli, and a French father, Alain de la Falaise.
After growing up in London and New York, she became a fashion writer, photographic model and designer, and met Saint Laurent in 1968, joining his house four years later.
Saint Laurent praised her for her charm and perceptiveness as well as her talents as a designer, whose work was noted for its contrasts and range of colours.
"Accessories have an important role in our stressful lives," she once said. "If you're going out to dinner and you haven't had the time to go home to change, you can take off your jacket and put on some jewellery."
She adored brightly-coloured stones, huge enamel flowers and hearts in rock crystal, considered her "lucky" material.
After a brief marriage at the age of 18 with an Irish aristocrat, Desmond Fitzgerald, she married Thadee Klossowski de Rola, son of the painter Balthus, in 1977.
They had one daughter, of whom Saint Laurent was the godfather.
When the couturier retired in 2002, Loulou de la Falaise launched her own brand but also created jewellery for other firms, as well as for the shop at the Majorelle Garden in Marrakesh, where Saint Laurent's ashes were scattered after his death in 2008.