Ian Williams will join personal finance website Moneysupermarket.com as director of comms, responsible for investor relations, consumer and international PR.
Williams has worked with Moneysupermarket.com since 1999, when it was one of Lansons' first digital clients in the dot com boom.
He was instrumental in defending the website last year amid allegations that price comparison sites like Moneysupermarket.com mislead customers .
Williams will leave next month, with director Rebecca Mayo taking over his role alongside joint MD Laura Hastings.
Mayo has been at Lansons since 1999, and joined the executive committee two years ago.