The Ravens have reportedly bolstered their defensive line again early in free agency.
Spears tweeted the news, saying, "I'm a raven!! See u in Maryland God is so good."
The team announced Friday that they reached an agreement in principle on the two-year deal.
"He brings a lot of snaps and big game experience to us," General Manager Ozzie Newsome said. "We like the way Marcus plays. He will fit in with the Ravens way of playing."
Spears, 30, was released after eight seasons in Dallas, just two years after signing a five-year, $19.2 million contract.
He was released after Dallas decided to move to a 4-3 defensive scheme with new Defensive Coordinator Monte Kiffin. Spears is more suited to play defensive end in a 3-4 package.
Spears played in 15 games last season, but made just six starts. He finished the year with 35 tackles, one sack and two tackles for loss. He posted 10 sacks in his eight seasons in Dallas.
Spears was a full-time starter his first six years as a Cowboy but lost that after a strained calf ended his season early in 2010.
The 6-foot-4, 315-pound former first-round pick from LSU will add size to the Ravens' front line. He'll also join another former Cowboys teammate and recent Ravens signing, Chris Canty, to give Baltimore more experience and run-stopping force up front.
"The base of a good defense is to be good along the defensive line," Newsome said. "We didn't play to our standards last season, partly because of injury. With the expected better health of players like Haloti Ngata and Pernell McPhee and the additions of Marus Spears and Chris Canty, we have a chance to improve. Spears, like Canty, can play multiple positions along the line."
Spears and Canty both came into the league at the same time with Dallas in 2005. Spears was a first-round pick and Canty was a fourth rounder. During their four years together, the Cowboys' run defense ranked 15th, 10th, 6th and 12th in the league, respectively.
The Ravens finished last season ranked 20th against the run (122.8 yards per game), and although they've lost several free agents already this offseason, they have made two moves to solidify their defense up front.