Stewart will stay on as the chairman and chief executive of the Milton Keynes-based team he set up with his son Paul, who will remain as deputy chairman.
"Ford's increased commitment to Formula One is great news for the team," said Stewart, who retired from racing after winning his third world title in 1973. "To be competitive in Formula One these days, and to win the great benefits available, a team needs strong financial and technical support. Ford can offer that."
Jac Nasser, Ford's chief executive officer and president, said: "Ford Motor Company has a long and very successful record in auto racing. Our latest move will allow us to take our performance to the next level."
Neil Ressler, Ford's chief technical officer who is also a director of Stewart Grand Prix, added: "By buying our own team, and applying the company's comprehensive technical resources to it, I believe the Stewart-Ford team will become increasingly more successful."
Stewart won 27 times in his 99-race career before bringing his retirement forward by missing the final race of the 1973 season in America when Tyrrell team-mate Francois Cevert was killed during practice.
He maintained his close association with Ford during his retirement, however, and secured an exclusive five-year engine deal with the company when he set up Stewart Grand Prix in 1996 with his son.
The team made its debut at the Australian Grand Prix in 1997 and scored its first podium that year when Rubens Barrichello finished second in Monaco.
Stewart-Ford are currently sixth in the manufacturers' championship.Reuse content