Mason called team owner Steve Bisciotti on Saturday morning, expressing his desire to return. The 35-year-old Mason showed up at training camp after the morning practice session and met with general manager Ozzie Newsome.
The Ravens then announced that Mason would be in uniform for Sunday's practice.
"It was a tough decision, but I think it was a good decision for me to come back," Mason said in a statement. "I needed to evaluate my life, football and my career.
"I still have an intense fire inside me, and I want to play. ... I felt like I had left something undone, and I wanted to finish it. I believe this is a good example for my son and my daughter on how to be thoughtful and also follow through."
On July 13, Mason said, "After 12 years, I have seen it all and done it all. Right now, I am content with the decision I am making. All good things come to an end, and I am ready to see what else life has to offer."
But Mason never submitted his retirement papers to the NFL, and within days it became clear that he was waffling over his decision to quit.
Mason and coach John Harbaugh met last week, and Harbaugh emerged from the session "optimistic" that Mason would return.
Mason played a key role in helping Baltimore reach the AFC title game last season. He started all 16 games and led the Ravens in receptions (80) and yards receiving (1,037). He then added 12 catches for 190 yards and a touchdown in three playoff games.
After playing eight seasons with the Tennessee Oilers/Titans, Mason joined the Ravens as a free agent in March 2005. Last season the two-time Pro Bowler became the 31st player in NFL history to reach 10,000 career yards receiving.
Copyright 2009 by The Associated Press