BARCELONA, Spain — THE speech, before hundreds of thousands of pro-independence Catalans, was as straightforward as the seven-mile-long V for vote that the crowd formed along two of the main avenues of Barcelona, Catalonia’s regional capital.

“We will vote, and we will win,” the speaker, Carme Forcadell, a teacher and onetime local politician turned street activist, told the cheering demonstrators in September on the Diada, Catalonia’s national day. She stood on a podium with her hand raised and fingers spread to make a V, this time for victory.

While Catalonia is scheduled to hold a significantly watered-down referendum on secession on Sunday, the region remains far from breaking away from the rest of Spain. The vote has been fiercely opposed by Madrid and, after a ruling on Tuesday by Spain’s Constitutional Court suspending it, may not be recognized at all.

But as the president of the Catalan National Assembly, a citizens’ platform that started organizing pro-independence events two years ago, the feisty Ms. Forcadell has helped ensure that Catalonia’s secessionist drive has turned into the biggest issue facing Mariano Rajoy, Spain’s prime minister.