Alaïa’s career started with a part-time job finishing hems (assisted at first by his sister, who also studied fashion). He became a dressmaker’s assistant, helping to copy couture gowns by such Parisian couturiers as Christian Dior, Pierre Balmain, and Cristóbal Balenciaga for wealthy Tunisian clients.
In 1957 Alaïa moved to Paris and worked on two collections at Guy Laroche, learning the essentials of dress construction.  Between 1960 and 1965 he lived as a housekeeper and dressmaker for the comtesse Nicole de Blégiers and then established a small salon on the Left Bank, where he built up a devoted private clientele. 

By the 1970s, in response to the changing climate in fashion, Alaïa’s focus shifted from custom-made gowns to ready-to-wear for an emerging clientele of young, discerning customers. Toward the end of the decade he designed for Thierry Mugler and produced a group of leather garments for Charles Jourdan. In 1981 he launched his first collection; already favored by the French fashion press, he soon found international success. In 1982 he showed his prêt-à-porter, or ready-to-wear, line at Bergdorf Goodman in New York, and in 1983 he opened a boutique in Beverly Hills.

The French Ministry of Culture honored him with the Designer of the Year award in 1985. He has dressed many famous women, such as the model Stephanie Seymour, the entertainer and model Grace Jones, and the 1950s Dior model Bettina. Moreover, Alaïa was the first to feature the supermodel Naomi Campbell on the catwalk.

Alaïa’s technique was formed through traditional couture practice, but his style is essentially modern.

He is best known for his svelte, clinging garments that fit like a second skin. Although he is revered in the early 2000s, the 1980s were in many ways Alaïa’s time; his use of stretch Lycra, silk jersey knits, and glove leather and suede suited the sports- and body-conscious decade. Alaïa has described himself as a bâtisseur, or builder, and his tailoring is exceptional. He cuts the pattern and assembles the prototype for every single dress that he creates, sculpting and draping the fabric on a live model.

As he explains:

“I have to try my things on a living body because the clothes I make must respect the body”. 

Although his clothes appear simple, many contain numerous discrete components, all constructed with raised, corsetry stitching and curved seaming to achieve a perfect sculptural form.

Alaïa produced a stunning variety of fashions. They included jersey sheath dresses with flesh-exposing zippers, dresses made of stretch Lycra bands, taut jackets and short skirts, stretch chenille and lace body suits, leggings, skinny jumper dresses with cutouts, and dresses with spiraling zippers. To this oeuvre he added bustiers and cinched, perforated leather belts; cowl-neck gowns; broderie anglaise or gold-mesh minidresses; and stiffened tulle wedding gowns. His palette favored muted colors, in particular, black, uncluttered and unadorned with jewelry.

Alaïa was a perfectionist and had been known to sew women into their outfits in order to get the most perfect fit. In 2000 Prada acquired a stake in Alaïa; the agreement contains the promise of creating a foundation in Paris for the Alaïa archive, which includes not only his own creations but also designs by many twentieth-century couturiers, such as Madeleine Vionnet and Cristóbal Balenciaga.

Alaïa said,

“When I see beautiful clothes I want to keep them, preserve them?. clothes, like architecture and art, reflect an era”.