HELSINKI—The euroskeptic leader of Finland's nationalist party, the Finns Party, will become foreign minister in a three-way coalition cabinet that has vowed to repair the country's recession-choked economy through deep spending cuts.

The Finns Party leader, Timo Soini, will serve in the government of Juha Sipila, who is set to become Finland's next prime minister after leading his centrist party to victory in last month's general election.

Departing Prime Minister Alexander Stubb, an avowed supporter of the European Union, will be the coalition government's finance minister.

The political rise of Mr. Soini, from head of a fringe party to senior government minister, is emblematic of the wider surge in anti-EU forces recorded across the continent. Mr. Soini's presence in the Finnish government could complicate talks between Greece and its creditors over the Mediterranean country's debt load because the nationalist politician has been a staunch opponent of the Greek bailouts.

"Finland respects common rules and expects other member states to do same," Mr. Soini told reporters on Wednesday.

Yet, Finland has been mired in economic recession for the past three years, making it harder for Finnish politicians—whether in the opposition or in office—to lecture other EU countries on economic policies.

On Wednesday, Mr. Soini appeared to tone down some of his anti-EU rhetoric. The politician, who has drawn inspiration from British-style euroskepticism, said the incoming government doesn't see any need for changes to the main treaties that form the legal base of the EU.

The future government doesn't "regard the amendment of treaties as a priority," Mr. Soini said.

Mr. Sipila's government has proposed implementing spending cuts and other fiscal adjustment measures that will amount to 4.0 billion euros ($4.4 billion) in aggregate by 2019, or about 2% relative to Finland's national output.

The fiscal adjustment program is aimed at stopping a rise in Finland's ratio of public debt to national output by 2019 and to close Finland's public funding gap by 2021.

Finland's prolonged economic stagnation has resulted in recurring budget deficits which will push the country's debt-to-GDP ratio to 62.6% this year, according to the European Commission's latest forecast, from 32.7% in 2008.

Breaching the 60% debt ceiling set in the European Union's fiscal rules has been an embarrassment for Finland, which aligned itself with Germany as a stern advocate of fiscal discipline during the eurozone's debt crisis.

Finland's previously high-performing economy has suffered from permanent output losses in the manufacture of mobile handsets and paper, formerly bedrock industries. The economy, which was in recession between 2012 and 2014, is also held back by high labor costs, a rapidly aging population, and EU sanctions against one of its top trade partners, Russia.

Write to Juhana Rossi at juhana.rossi@wsj.com

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