Mikati, an opposition-backed former public works minister, won the position after President Emile Lahoud polled legislators or their representatives from the 128-member parliament.
Mikati, a 49-year-old wealthy businessman and friend of Syrian President Bashar Assad, won the largest number of votes, telling reporters 58 lawmakers gave him their support, the Associated Press reported.
The number of those who backed his opponent, staunchly pro-Syrian Defense Minister Abdul-Rahim Murad, was not revealed.
“We will be the symbol of moderation and national unity,” Mikati said from the presidential palace after being appointed by Lahoud.
“I say it from here that the hand is extended and the heart is open so that we all cooperate in the Lebanese interest,” he said, according to the AP.
Lebanon has been without a government since Omar Karami resigned as prime minister on Feb. 28 amid anti-Syrian protests sparked by the assassination of former Prime Minister Rafik Hariri.
Lahoud named Karami to try to build a new cabinet, but failed after weeks of negotiations.
Mikati must form a government, win a confidence vote in parliament, draft an election law and get it passed by the assembly all in under two weeks to have enough time to hold elections by May 31, according to Reuters.
The opposition had accused the pro-Syrian leadership of trying to scuttle the vote and keep the Damascus-dominated legislature in place, reported the AP.
The United States has led international calls to hold the parliamentary elections on time.
“It’s in the interest of Lebanon, in the interest of the people of Lebanon, in our view, that these elections take place quickly and we hope that the cabinet formulation will take place quickly,” U.S. ambassador to Lebanon Jeffrey Feltman said before Mikati’s appointment, Reuters reported.