At a national convention of the party in Warsaw, 340 delegates voted for Kidawa-Błońska, who is expected to take on incumbent conservative President Andrzej Duda in May.
A total of 125 delegates on Saturday voted for Kidawa-Błońska’s rival within the Civic Platform, Jacek Jaśkowiak, the mayor of the western city of Poznań.
The vote was the last stage of a primary election within the Civic Platform, which is Poland’s biggest opposition grouping, to select a contender.
Kidawa-Błońska has presented herself as a moderate, conciliatory figure able to reach out to voters from across Poland’s bitterly divided political landscape.
She said after Saturday’s vote: “We will win this election.”
She added: “From today we are working for victory… we can win and we will win in May.”
Poland’s ruling conservatives last month reaffirmed their support for incumbent President Andrzej Duda, who is expected to seek re-election in May.
Ex-European Council President Donald Tusk, a former Polish prime minister, has previously declared he would not run for president next year.
Kidawa-Błońska was an opposition candidate for prime minister in the country’s parliamentary elections on October 13.
That ballot was won by Poland's ruling conservatives, who secured a second term in power.
Meanwhile, the leader of the opposition Polish People’s Party (PSL), Władysław Kosiniak–Kamysz, on Saturday also announced he would stand for president next year.
He said: “I believe deeply that we can change Poland for the better, that we are prepared to fight for a better Poland for everyone, not for the select few.”