Conte whose continuation was one of the key demands of the anti-establishment M5S when it took up talks with the Democratic Party (PD) was the first to pledge loyalty to the Republic and the Constitution at the Quirinale, the presidential palace.
The new government will feature 10 Ministers from the M5S, nine from the PD, one from the left-wing Free and Equal, one independent technocrat, according to Efe news.
They all took oath in the presence of Italy's President Sergio Mattarella and are later expected to hold a first Cabinet meeting.
Notable appointments included the M5S leader Luigi di Maio's posting as Foreign Minister. The Interior Ministry, previously the haunt of Matteo Salvini of the far-right League party, will now be occupied by Luciana Lamorgese, an independent.
Alfonso Bonafede (M5S) will take on the Justice Ministry, Lorenzo Guerini (PD) will head to the Defence Ministry and Roberto Gualtieri (PD) will head the Economy Ministry.
Di Maio on Wednesday said the new government would be "brave and ambitious, able to carry forward important measures for the growth and development of Italy".
Italy teetered on the brink of another political crisis when in August erstwhile Interior Minister Salvini called an end to the M5S-League coalition and pushed for a snap election at a time when his party polled high.
Instead, the M5S opened talks with the PD, which had been battered in the previous general elections.
Salvini had railed against the new government, insisting in a tweet on Thursday that it would not last long. The firebrand politician became notorious for his staunchly anti-immigration policies while serving as Interior Minister.
The PD's leader, conversely, wished the new government well. "Good work and best wishes to the new Government and to all the Ministers! Now let's change Italy," he tweeted.
( With inputs from IANS )