The relationship started in 1964, when Stewart accelerated a Ford power plant in grands prix, before accompanying him to team ownership, a role at Jaguar, to the present ambassadorial day.
Ford said it and the 65-year-old Scot would not renew the deal for 2005.
"It's the right time for me and Ford to start a new chapter with new challenges," the triple world champion commented, claiming that the 'intensive' time commitment is becoming 'difficult to manage.'
Company founder Henry Ford's great grandson, Edsel B. Ford, paid tribute to Jackie's 'tremendous impact' to the fabled carmaker. "He has been much more than a consultant," he said. -GMM