The gathering in a former museum in the southern French city, which goes on until Sunday, comes ahead of the first anniversary of the protests on November 17.
“We need to do something that stands out” to mark the date, said Fabienne, a delegate from Grenoble who like others attending gave only her first name to reporters.
Jacques, a delegate from Lille, said: “This assembly shows the extent of the yellow vest movement.”
Some 200 delegations are expected at the assembly, which will include a series of workshops to discuss issues such as how to respond to heavy-handed police tactics or how to work with other protest movements.
“We started out amid heavy repression… with a sense of urgency to solve problems. Now is the time for longer-term work on a solid base,” said Christophe Chapuis, the assembly's designated spokesman.
French President Emmanuel Macron was caught out by the yellow vest protests when they started last year, as protesters accused him of ignoring the day-to-day struggles of ordinary French people.
The numbers have dropped far below the initial protest in November last year, which brought out more than 280,000 people across France.
But a dedicated group of activists maintain the Saturday demonstrations in cities around France, arguing that Macron is still ignoring the needs of marginalised groups such as the working poor.