Five defendants received prison terms of between eight and 10 years on Wednesday, while the others received lesser sentences.
Two were acquitted. All but one defendant had been accused of helping Islamist fighters in Chechnya in what prosecutors said underscored the "globalisation of the jihad movement".
Prosecutors could not prove that the attack was to have involved chemicals, but investigators found a protective suit and chemicals including ricin, which is toxic.
Menad Benchellali, the group's alleged chemicals expert, got the maximum 10-year term.
Menad's father, Chellali Benchellali, a prayer leader in the Lyon suburb of Venissieux, received an 18-month suspended prison term - far lower than the prosecution's demand for six years behind bars.
The court convicted 24 defendants of criminal association in relation to a terrorist enterprise, a broad charge used by France.
One other was convicted of using false papers.
The Benchellali family was at the centre of the case, with Menad's mother, Hafsa, and brother, Hafed, also on trial for roles in the plot to carry out an attack in France.
The network was dismantled in two waves, the first in December 2002 as investigators stormed two houses in the Paris suburb of La Courneuve and the nearby town of Romainville.
They found gas canisters, fuses, chemicals and a suit to protect against chemical attacks.
During a second wave of arrests in January 2004 in Venissieux, southeast France, investigators found chemical products, including ricin, and broke up the network.
The prosecution said the group was plotting an attack in Paris, but could not define the target. The Russian embassy, a police station and the Eiffel Tower were mentioned during interrogations.
Profiting the US
Isabelle Coutant, lawyer for defendant Merouane Benhamed, said: "These convictions profit the United States, Algeria and Russia. They have been convicted because they are Muslims."
Prosecutor Anne Kostomaroff, profiling the network, put the origins of the group in Chlef, Algeria, in 1999, where eight members had refused an Algerian government amnesty plan for Islamist insurgents in the North African country.
Various members then travelled to Spain, France, Italy and the border region between Pakistan and Afghanistan, while a core group formed in the Paris region in late 2000 to create a support ring for separatists in the Russian republic of Chechnya.