Saatchi X spokeswoman Betsy Reithemeyer said Mr. Murray announced his intention to step down as executive chairman last month; his resignation was effective with the start of the agency's fiscal year Jan. 1. He will concentrate on the marketing-focused new-business incubator he founded last year, Mercury 11, which is based near Saatchi & Saatchi X's headquarters in Fayetteville, Ark., she said.
Mr. Murray couldn't immediately be reached for comment.
A former sales executive on P&G's dedicated Walmart Stores team, Mr. Murray left P&G to form a consulting firm in 1997 and in 1999 merged it with a northwest Arkansas advertising agency to create Thompson Murray, one of the first shopper-marketing agencies.
Ms. Howell, marketing director on P&G's Walmart team, was an early client. Publicis Groupe 's Saatchi & Saatchi acquired the agency in 2004; it now has 375 employees in 14 offices and 11 countries, with P&G and Walmart among its top clients.
Ms. Howell left her position as VP-global media and brand operations at P&G in 2010 to become worldwide CEO of Saatchi X.