The announcement, made after an emergency cabinet meeting, was an unexpectedly forceful attempt to stop a yearslong drive for secession in Catalonia, which staged a highly controversial independence referendum on Oct. 1., even after it was declared illegal by the Spanish government and courts.

Mr. Rajoy took the bold steps with broad support from Spain’s main political opposition, and will almost certainly receive the required approval next week from the Spanish Senate, where his own conservative party holds a majority.

But the moves were immediately condemned by Catalan leaders and thrust Spain into uncharted waters as the prime minister tried to put down the gravest constitutional crisis his country has faced since embracing democracy after the death of its dictator Gen. Francisco Franco in 1975.