A member of the Savelli family, Giacomo Savelli was born in Rome in 1523, the son of Roman nobles Giambattista Savelli and Costanza Bentivoglio.[1] His paternal grandmother, Camilla Farnese, was a cousin of Pope Paul III.[1]
Savelli studied Latin and Greek as a young man and then attended the University of Padua to study law.[1] He joined the papal household of Pope Paul III as a chamberlain of honor.[1] He also served as a protonotary apostolic.[1]
Pope Paul III made him a cardinal deacon in the consistory of 19 December 1539.[1] He received the red hat and the deaconry of Santa Lucia in Selci on 16 April 1540.[1] On 8 January 1543 he opted for the deaconry of Santi Cosma e Damiano.[1] From 13 April 1545 to 26 May 1546 he was the administrator of the see of Teramo.[1]
He participated in the papal conclave of 1549-50 that elected Pope Julius III.[1] The new pope made Cardinal Savelli papal legate in the March of Ancona and he served in that position throughout the pontificate of Julius III.[1] He opted for the deaconry of San Nicola in Carcere on 9 March 1552.[1]
He participated in both the papal conclave of April 1555 that elected Pope Marcellus II and the papal conclave of May 1555 that elected Pope Paul IV.[1]
He was the administrator of the see of Gubbio from 29 May 1555 until 6 February 1556, when he resigned the administration in favor of his nephew Marino Savelli, bishop-elect of Nicastro.[1] Cardinal Savelli became administrator of Nicastro for a second time starting 6 February 1556, resigning sometime before 26 January 1560.[1]
On 16 December 1558 he opted for the deaconry of Santa Maria in Cosmedin.[1] In 1559, he participated in the papal conclave that elected Pope Pius IV.[1]
He was ordained as a priest on 19 January 1560, and he opted for the order of cardinal priests at that time.[1] From 26 January 1560 until 17 May 1574 he was administrator of the see of Benevento.[1] He was also the Vicar General of Rome from 1560 to 1587.[1] On 27 June 1571 he was one of three cardinals appointed by the pope to study providing assistance for the poor of Rome.[1] He participated in the papal conclave of 1565-66 that elected Pope Pius V.[1] He served as Camerlengo of the Sacred College of Cardinals from 14 January 1568 until 14 January 1569.[1] He was a participant in the papal conclave of 1572 that elected Pope Gregory XIII.[1] On 8 April 1573 he opted for the titular church of Santa Maria in Trastevere.[1]
On 31 July 1577 he opted for the order of cardinal bishops, receiving the suburbicarian see of Sabina.[1] He opted for the suburbicarian see of Porto e Santa Rufina.[1] During this period, he was the Vice-Dean of the College of Cardinals.[1]
In 1585, he attended the papal conclave that elected Pope Sixtus V.[1] He died in Rome on 5 December 1587.[1] He was buried in the Church of the Gesù.[1]