The ceremony brought long sought-after stability to the country following months of political drama that had anxious financial markets and Italy's European Union partners. The government is expected to win.
Its ambitious economic proposals - which include a monthly basic income for Italy's poorest and a two tier "flat" tax - have anxious Brussels and financial markets given Italy's massive 2.3 trillion euro ($2.7 trillion) debt.
A controversial agreement between Italy's former centre-left government and authorities and militias in Libya has triggered a decline in overall arrivals of some 75 percent since the summer of 2017.
Next week the government faces mandatory confidence votes in each chamber of Parliament, where the coalition members hold narrow, but viable majorities.
The continent's euroskeptic politicians cheered the birth of the new Italian government coalition of the 5-Star Movement and the right-wing League party.
After the initial attempt to form a government failed, Mattarella picked Carlo Cottarelli as interim prime minister.
The president approved Conte and a rejiggered Cabinet list Thursday after Paolo Savona was moved from the economy slot to that of the ministry of European affairs.
Italy's new interior minister says the island of Sicily will no longer be what he calls "Europe's refugee camp".
Conte, 53, who has been criticised as being a "Mr Nobody", named hardline anti-migrant Salvini as interior minister, while Di Maio is minister for economic development.
Conte has been appointed prime minister and, along with his cabinet, will be sworn in on Friday.
Migration experts have stated that the appointment of such a radical leader will reduce rights of migrants and asylum seekers, in a country that already has difficulties in integration.
Financial markets bounced back Friday after a rollercoaster ride.
One protester brandished a sign saying "refugees welcome", while a supporter said "we don't want any more pests" and others simply chanted "Matteo, Matteo".
Its ambitious economic proposals - which include a monthly basic income for Italy's poorest and a two tier "flat" tax - have anxious Brussels and financial markets given Italy's massive €2.3 trillion debt. "There's no easy option if Italy needed help tomorrow".