Trzaskowski, a candidate backed by the opposition Civic Coalition, an alliance between the Civic Platform (PO) and Nowoczesna (Modern) parties, won a decisive, first-round victory in the race for mayor after garnering 56.67 percent of the vote, the commission said.
Some pre-election surveys had suggested the battle for Warsaw would need to go to a second round.
Conservative candidate Patryk Jaki, who some observers said appeared to be running neck and neck with Trzaskowski in the polls ahead of Sunday’s local government elections, finished runner-up with 28.53 percent of the vote, the commission reported.
A total of 505,187 Varsovians cast their ballots to support Trzaskowski, while 254,324 voted for Jaki, the commission said.
The 12 other mayoral hopefuls received marginal support, with the third and fourth finishers each winning just 2.99 percent of the vote, the National Electoral Commission said.
Voter turnout in Warsaw was 66.8 percent, compared with 54.96 percent nationwide, the commission announced.
Meanwhile, mayoral races in several other major cities, including the southern city of Kraków, were inconclusive and going into run-offs.
Poland's ruling conservatives were outdistanced by the opposition in mayoral races in several major cities, including Łódź, Poznań and Wrocław, with no need for a second round there, the National Electoral Commission said.
A second round of voting, where needed, will be held on November 4.
Run-offs between the two most popular mayoral contenders will take place where the winning candidate failed to garner more than 50 percent of the vote in the first round.
Meanwhile, the ruling conservative Law and Justice (PiS) party has won the most votes in elections to Poland’s regional assemblies, the country's PAP news agency reported earlier this week, citing what it described as a "late poll."
The official results of the regional vote were expected to be announced later on Wednesday.