Young, 34, has a 53-43 record and a 3.79 ERA over parts of nine seasons with Rangers, Padres and Mets. He pitched well for the Nationals this spring, with a 3.48 ERA in four outings, before accepting his release Tuesday after it became clear he would not be in the team's Opening Day rotation.
Young had surgery to correct thoracic outlet syndrome last summer after two shoulder operations, and his fastball was clocked as high as 88 mph in the Grapefruit League. That was significantly higher than the 84.6 mph he averaged with the Mets in 2012.
Hisashi Iwakuma and Taijuan Walker will begin the season on the disabled list, and two other veteran pitchers parted ways with the team earlier this week. Scott Baker signed with the Rangers after being released by Seattle, and Randy Wolf opted for free agency rather than sign a waiver that would have allowed the Mariners to release him in the first 45 days of the regular season without having to pay his full salary.
The Mariners designated pitcher Bobby LaFromboise for assignment to make room for Young on the roster.