Pierleoni led the defence of the city against Pope Lucius II's assault in 1145, where Lucius himself was killed. However, Pierleoni was unable to maintain order in the city despite his overtures of negotiations with Lucius—demanding the pope renounce secular authority and live as a common priest before being allowed reentry into the city, —he was deposed by the people who invited Pope Eugene III, Lucius' successor, back.
Pierleoni successfully defended the city against Pope Lucius II's 1145 assault, but ultimately lost control of the city despite his efforts to negotiate with Lucius. The people eventually deposed Pierleoni and invited Pope Eugene III to take over, following in Lucius' footsteps.