The team announced Thursday the hiring of McDowell, who will replace Landon Cassill, as well as an increased technical relationship with Ford and Roush Fenway Racing.
McDowell was 26th in the standings in 2017 and found out in September that he would not have a ride in 2018 as Leavine Family Racing decided to hire Kasey Kahne after his release from Hendrick Motorsports.
McDowell drove for Front Row Motorsports in 2013 at Watkins Glen. He has one career NASCAR national series win, driving for Richard Childress Racing in the August 2016 Xfinity Series race at Road America.
Having posted five top-10s in 249 career Cup starts with a best of fourth at Daytona in July, McDowell views road courses and restrictor-plate events as potential victories that could qualify him for the NASCAR playoffs.
"Since I first drove for Bob at Watkins Glen, we've kept in touch and have felt like there might be an opportunity to work together again, and the timing worked out perfectly," McDowell said. "It's been a while since I've had a teammate, so I'm really looking forward to working with David, whom I've become pretty good friends with over the years.
"As a team now, we go into the season knowing we have five or six races that put us in position to get a win and earn a spot in the playoffs."
Cassill, who found out in October that he would not be retained, is still looking for a ride for 2018. He was 31st in the standings in 2017, one spot -- but 65 points -- behind Ragan.