Salam, who won sweeping parliamentary endorsement, will immediately be tasked with preparing the ground for a parliamentary election, due in June after forming a government.
In his first comments after appointment, Salam said he would seek to "unite opinion and reach speedy agreement on a parliamentary electoral law to achieve fair representation for all citizens and sects".
He also pledged to focus on "ending Lebanon's political divisions and its impact on the security situation, and averting the dangers from the neighboring tragedy (in Syria) ".
Salam was chosen as a consensus candidate acceptable to Hezbollah and March 14 groups.
"I will absolutely strive to form a government of national benefit", he said referring to speculation over whether his government should be a short-term technocratic administration focused only on preparing for elections, or a 'national unity' government with longer-term ambitions.