Thiam received votes from over 90% of the 7,000 assembled members of the PDCI, the French acronym for Democratic Party of Ivory Coast, the party said.
Thiam, 61, served in the cabinet of ex-President Henry Konan Bedie in the 1990s before leaving the West African country almost 25 years ago when Bedie was ousted in a coup.
Since then he has worked for consultancy firm McKinsey, insurers Aviva and Prudential and as Credit Suisse CEO. He quit the Swiss bank in 2020 following a major spying scandal in which he denied any involvement.
PDCI governed Ivory Coast from independence to the early 2000s. Its previous party leader Bedie died in August aged 89.
The last presidential poll in 2020 ended an alliance between President Alassane Ouattara's RDR and PDCI, after an election that opposition parties largely boycotted and dismissed as illegal. Clashes in the run-up to the vote and on election day killed around 35 people.
Ouattara, 81, has not stated his intentions for 2025.
(Writing by Anait Miridzhanian and Alessandra Prentice; Editing by Leslie Adler and Richard Chang)
By Ange Aboa
