The Florida Supreme Court ruled Friday that the death penalty cannot be imposed without the unanimous support of a jury, deepening the recent turmoil around capital punishment in a state with a long history of executions.

One of Friday’s decisions, in a case that previously reached the United States Supreme Court and upended Florida’s death penalty system, said that the Eighth Amendment, which forbids cruel and unusual punishment, and Florida state law effectively mandated consensus in capital cases. The court said in a separate case that a new state law, which allowed for the death penalty when 10 of 12 jurors agreed, was unconstitutional.

“Requiring unanimous jury recommendations of death before the ultimate penalty may be imposed will ensure that in the view of the jury — a veritable microcosm of the community — the defendant committed the worst of murders with the least amount of mitigation,” the Florida court said in siding with Timothy L. Hurst, a death row inmate whose appeal led lawmakers early this year to rewrite the state’s death penalty law.

Referring to a 1958 United States Supreme Court opinion invoking the Eighth Amendment, the Florida court added, “This is in accord with the goal that capital sentencing laws keep pace with ‘evolving standards of decency.’”