Giovanni Battista Mellini was born in Rome on 9 June 1405, the son of a noble family.
[1] He resigned this canonry during the pontificate of Pope Nicholas V, who made him economous of St. Peter's Basilica.
[1] He received the red hat and the titular church of Santi Nereo e Achilleo on 30 December 1476.
[1] On 1 January 1477 the pope named him papal legate in the Duchy of Milan and Lombardy, with full powers to keep following the 26 December 1476 death of Galeazzo Maria Sforza.
[1] He was buried in St Peter's Basilica but his tomb was later transferred to the Mellini family chapel in Santa Maria del Popolo.