According to the eastern European country's electoral body, the center-right former physics professor obtained 62.8 percent of the votes, while Social Democrats’ (PSD) Dancila received the other 37.1 percent.
"The winner today is modern Romania, European Romania, normal Romania," Iohannis told reporters in his victory speech, adding that he received "this victory with joy, thankfulness, modesty and with faith in Romania."
The general participation represented 49.87 percent, as a total of 18.2 million Romanians were eligible to vote including a record 650,000 voters living abroad.
Ahead of Sunday's vote, 60-year-old Iohannis, whose victory confirms the country’s pro-European trajectory, pledged to fight corruption, to build functioning institutions and to restart judicial reform with allies in the new, center-right government led by the center-right National Liberal Party (PNL).
The successive PSD governments had been involved in a long battle with the European Union over allegations the party was trying to impose measures to neuter the judiciary. Iohannis had sided with Brussels during the controversy.
The left-wing party, which was considered by a part of the population to be the replacement of the ruling elite before the fall of communism, had also been accused of widespread corruption.