The deal will be for $26 million with a team option that has a $1 million buyout, reports Jim Bowden of ESPN.
Ross, 31, hit 22 home runs last season for the Red Sox, primarily playing left and right field. The outfielder hit his way to an OPS of .807.
The deal may be a signal of a trade to come, as the Diamondbacks now have Ross, Justin Upton, Jason Kubel, and promising center field prospect Adam Eaton. The team has reportedly been in talks involving both Kubel and Upton.
Ross played for the Tigers, Dodgers, Reds, Marlins, and Giants before coming to the Red Sox on a one-year contact. He won the National League Championship Series MVP award in 2010 as a member of the San Francisco Giants, who claimed him on waivers that August.