Twister is representing the Turin-based bank in its proposed merger with Banca Intesa of Milan, expected to be completed next year. The deal will create an institution worth around £43bn.
Agency MD Gabriele Lucentini heads the account, reporting to Sanpaolo chairman Enrico Salza. Banca Intesa is using its in-house comms team.
City watchers believe the merger could prompt a wave of Italian activity in this area, with the country's fourth-largest bank, Capitalia, expected to be a target.