Omnicom's PHD is poised to win HSBC's estimated $400m (£298m) global media planning and buying account.
Mindshare has held HSBC for 13 years, having successfully defended the account most recently in 2013, and the loss would be a blow to parent company WPP, which is searching for a chief executive to replace Sir Martin Sorrell.
PHD is said to have beaten Mindshare and Dentsu Aegis Network in a three-way contest.
Industry sources said agency groups have been told about the outcome of the review. ID Comms advised on the pitch.
None of the groups would comment and referred inquiries to HSBC.
A spokesman for HSBC did not immediately comment.
HSBC's key markets include the UK, US, China and the Middle East.
HSBC previously announced the review in January when it said: "As part of our commitment to the ongoing development of HSBC’s media and marketing arrangements, we periodically evaluate all marketing service suppliers to ensure we maintain the best working relationships to support our strategic goals."
The bank appointed former senior Mondelez International executive Leanne Cutts as group head of marketing last year.
HSBC began the review several months before Sorrell quit as chief executive on 14 April.
WPP has had a close relationship with HSBC, which uses J Walter Thompson for creative duties as well as Publicis Groupe's Saatchi & Saatchi.