Longoria posed for photographers before entering the city hall
The couple are thought to be holding a second ceremony at a Paris church - followed by a star-studded party at a 17th Century chateau - on Saturday.
Paris mayor Bertrand Delanoe confirmed he had conducted the civil ceremony.
French law requires couples to exchange vows at a city hall, even if they have a church wedding as well.
Longoria, 32, showed up first in a white stretch limo, wearing a short pink Chanel dress. It is thought she changed into a white dress once inside the venue.
She smiled and waved for a crowd of waiting photographers and reporters who were kept well back behind two rows of police barriers.
Parker, the 25-year-old San Antonio Spurs star who was born in Belgium and grew up playing basketball in France, arrived about 10 minutes later in a grey mini van, wearing a dark suit.
They were joined by a handful of guests, including French footballer Thierry Henry, for the short ceremony.
The couple have secured a deal to sell their wedding photos to OK! magazine for a reported $2m (£994,319).