"Could not be happier to be in the Dbacks family! Truly Blessed!" Ross posted on his Twitter account.
Ross, who turns 32 on Sunday and lives in nearby Scottsdale, adds to the abundance of outfielders on the Arizona roster, leading to speculation a trade might be coming. He batted .267 with 22 home runs and 81 RBIs last season for the Boston Red Sox. He's a career .267 hitter in nine big league seasons.
"I don't know what happened but we could never agree on terms," Ross told The Boston Globe. "They thought I'd come back no matter what because they thought I loved playing there. And I did. Who wouldn't love playing at Fenway Park? I just wanted a fair deal. I told them what I wanted. I wasn't trying to break the bank. They weren't willing to do it."
The addition gives the Diamondbacks four veteran outfielders -- Ross, Justin Upton, Gerardo Parra and Jason Kubel -- along with two youngsters the organization has deemed ready for the majors: Adam Eaton and A.J. Pollock.
The Diamondbacks are now working to trade Kubel, sources told ESPN. In his first season with Arizona last year, the left-handed slugger hit .253 with 30 home runs and 90 RBIs. He was hitting .300 on July 22 but batted .176 with 19 RBIs the rest of the season.
Upton also has been the subject of trade rumors this offseason.
Ross, who throws left-handed and bats right-handed, was a fourth-round draft pick of Detroit out of Carlsbad, N.M., High School in 1999. He had brief major league stints with the Tigers, Los Angeles Dodgers and Cincinnati before becoming a full-time big leaguer with the Florida Marlins.
Ross was claimed by San Francisco off waivers in August 2010 and was MVP of that year's NL Championship Series, hitting .350 with three home runs and five RBIs against Philadelphia. He also homered against Texas in the World Series and batted .294 (15 for 51) with five homers, five doubles and 10 RBIs in 15 postseason games for the champion Giants.
He committed one error in each of the last two seasons.
The Diamondbacks also announced that infielder Gustavo Nunez cleared waivers and was returned to Detroit, opening a spot for Ross on the 40-man roster. Nunez was claimed off waivers from Pittsburgh in October after the Pirates selected him from the Tigers in the 2011 Rule 5 draft.
Information from ESPN The Magazine's Buster Olney and The Associated Press was used in this report.