The Grey network has handled the business for over 50 years, making it one of most enduring creative partnerships.
CHI picked up the business following an internal WPP review process against Grey. Grey’s offices in New York and Dusseldorf have previously handled the account before arriving in London.
Sarah Golding, the chief executive of CHI, said: "To be on P&G’s roster for the first time and to work on a brand like Lenor is a big, big honour for CHI. And one that doesn’t come around every day. We are beyond delighted."
Lenor’s biggest markets in Europe are the UK and Germany.
Leo Rayman, the chief executive of Grey London, added: "I’m incredibly proud of the work our team put into the Lenor account.
"We continue to work in partnership with P&G across a large number of brands within their portfolio. We wish CHI the best of luck with the account."