Mark Carney’s predecessor as governor of the Bank of England on Thursday praised his handling of the U.K.’s decision to leave the European Union and declared confidence that London will remain the continent’s leading financial center.

But Mervyn King expressed pessimism about the global economic outlook and the eurozone’s prospects in particular, saying at an event hosted by The Wall Street Journal that both had been on an “unsustainable path” even before Britons voted on June 23 to leave the EU.

Mr. Carney has been widely criticized by politicians who campaigned to take Britain out of the EU over his warning in advance of the referendum that an economic slowdown and turbulence in financial markets would follow.

But Mr. King, who led the BOE from 2003 until 2013, said his successor and his other policy makers at the U.K.’s central bank had acted correctly and had “a moral and legal duty to give their view of the risks.”

He also said that tensions between the BOE and political leaders are likely to ease now that the campaign has ended.