With votes from all polling districts tallied, Nauseda received over 868,000 votes, or 66%, against Simonyte's 429,000, or 33%.
Nauseda's support doubled compared with the first round of voting two week ago, while his contender lost a part of votes.
"I hope that after a while, all the people of Lithuania, whom I'm grateful for the support, will feel they have won," Nauseda told reporters on Sunday night.
The newly-elected president vowed to work with the parliament and the government toward reducing the social divide in the country.
"I hope that together with other state institutions, we'll manage to find that common ground toward achieving one goal, which is making life in Lithuania better, making everyone in Lithuania feel better, ensuring that there is more mutual respect in Lithuania and less bullying, and that the old and the young, the better off and the worse off, someone who lives on the periphery and someone who lives in the center or the capital get along well with each other," he said.
The president-elect also hinted that he would soften the rhetoric toward Russia, but underlined that Lithuania's relations with Russia will not change substantially until Moscow alters its behavior toward Ukraine.
Nauseda said he would like to live in his own home in Pavilnys, a suburb of Vilnius, but he will have to discuss this issue with the VIP protection department.
Simonyte conceded her defeat and wished her rival "success in uniting all people".
The lawmaker said she will remain active in Lithuanian politics.
"Some 450,000 voters behind you is not someone to whom you can say easily, 'Thank you very much for the flowers and I'm going back to growing my daffodils," she told the public broadcaster LRT.
Lithuania's outgoing President Dalia Grybauskaite telephoned Gitanas Nauseda on Sunday night to congratulate him on victory and wished him "success in fulfilling voters' expectations".
