A billionaire former Czech Republic prime minister, Andrej Babis, seized on voters’ economic frustrations in his bid to reclaim power Saturday in parliamentary elections that could water down the country’s steadfast support for Ukraine and challenge the European Union and NATO on Russia.

Mr. Babis had linked the concerns of war-weary Czechs dealing with high consumer costs to his charge that the incumbent center-right government was spending too much on Ukraine. While the Czech economy is starting to stabilize, officials and experts said, the improvement came too late to resonate with voters.

As he now faces forming a new government — which could take weeks — Mr. Babis will have to decide how much leverage he will afford to right-wing Euroskeptics whose support he will need to push through his agenda. His party, Ano, which translates as “yes,” does not have a defined ideological bent, but leaders of the defeated center-right government have said they will not be part of an administration led by Mr. Babis, an all-things-to-all-people politician.

Mr. Babis must also contend with conflict-of-interest laws looming over his agribusiness companies before he can take office, and said on Saturday evening that he would “show a solution” to President Petr Pavel when the two men meet on Sunday.

Ano officials began popping wine corks and supporters cheered as Mr. Babis arrived to claim victory at the party’s headquarters in a suburban office complex that he owns.

“I am thrilled that we convinced people that it is only the Ano movement that has a clear vision for the future of our country,” Mr. Babis, said, exulting with 97 percent of the vote having been counted after two days of balloting that ended Saturday with a higher-than-usual turnout. He said he had not yet spoken to the outgoing prime minister, Petr Fiala.