Mengoni was just off the podium in Liverpool with his Sanremo winner Due Vite (Two Lives).
Sweden's Loreen became the first woman to win twice with Tattoo, after her victory in 2012 with Euphoria.
Loreen is the second person to win the extravanga of camp, kitsch and sometimes zany songs since Ireland's Johnny Logan in 1980 and 1987.
Finland won most of the phone-in popular vote to come a close second with Käärijä's entry Cha Cha Cha, while Israel came third with Noa Kirel's Unicorn.
Mengoni shot to fame in 2009 after winning the third season of the Italian version of The X-Factor.
He later won the San Remo festival in 2013, earning the chance to represent Italy at the 2013 Eurovision Song Contest in Sweden's Malmo. He performed the song L'Essenziale and finished in seventh place.
Mengoni won the Sanremo Festival for a second time in 2023, a decade after his last victory.
This year at Eurvision he earned the prestigious Marcel Bezençon Composer Award for the best musical composition.
The prize is awarded by the composers of the songs that compete in the final of the Eurovision Song Contest.
This is the second time Italy has won that award, following the 2019 success of Mahmood with his song "Money".
