BOGOTÁ, Colombia — Members of President Nicolás Maduro’s governing party marched triumphantly into Venezuela’s Capitol building on Friday, calling to order a 545-member body with plans to rewrite the Constitution and consolidate their power over the nation.

The constituent assembly, as the group is called, took a symbolic jab at their political rivals, parading through the gates of the legislative chamber holding portraits of former President Hugo Chávez, which were taken down just last year after opposition parties won control of the National Assembly.

“This assembly didn’t emerge from nothing,” said Delcy Rodríguez, a former foreign minister close to Mr. Maduro who will lead the body. “It has dodged the obstacles thrown in its way by those who resist democracy.”

The convening of the assembly was the culmination of an ambitious plan by the president to secure political control over Venezuela. In a contentious election on Sunday, Mr. Maduro instructed Venezuelans to choose delegates from a list of allies in the governing party. Voters were not given the option of rejecting the plan.