Jeffrey's appointment is expected to be formalised at a JWT worldwide management meeting in September. The 65-year-old Schweitzer will start a one-year spell as chairman after Jeffrey assumes the top job. Burt Manning will retain his titular role as chairman emeritus.
Jeffrey has been in line to lead the network since he was named by Schweitzer as the president for North America in 2001.
Jeffrey joined JWT in 1998, starting out as the president of the agency's New York office. Before joining JWT, he was the managing director at the San Francisco arm of Lowe & Partners, where he was responsible for launching the agency's West Coast operations - later to include clients such as Oral B and Sun Microsystems.
He spent two years in the position after having moved from Goldsmith/Jeffrey, the creative boutique he helped to found. After nine years of establishing a solid reputation as one of the top New York creative houses, through its work on accounts including American TV station ESPN and the bank JP Morgan, Goldsmith/Jeffrey was acquired by Lowe in 1996.
Jeffrey, now 48, started his career at Doyle Dane Bernbach in New York, where, over an eight-year period, he rose to the position of vice-president.
He has also been the executive vice-president at the US-based TBWA/Chiat/Day, where he oversaw work on Mitsubishi, Quaker and Sara Lee, among others.
Schweitzer - the lynchpin on WPP's largest single client, Ford - became the chief executive in January 2001. He previously served as the network's president, chief operating officer, vice-chairman, European vice-chairman and the general manager of JWT Detroit.
Schweitzer took over from Chris Jones, who stepped down for health reasons.