To make room on their 40-man roster, the Mariners designated left-handed reliever Bobby LaFromboise for assignment.
Young, who spent last year with Triple-A Syracuse in the Nats' organization, had surgery in June to repair thoracic outlet syndrome, an issue he believes had been causing shoulder problems that led to two prior surgeries. He posted a 3.48 ERA in four Grapefruit League appearances with Washington this spring, allowing eight hits and four runs with four walks and nine strikeouts in 10 1/3 innings.
Young is a nine-year Major League veteran with a career record of 53-43 and a 3.79 ERA, but he hasn't pitched in the big leagues since 2012 with the Mets, when he was 4-9 with a 4.15 ERA in 20 starts.
Young went 9-8 and ranked fifth in the National League with a 3.12 ERA with the Padres in 30 starts in 2007, but he hasn't pitched a full season since, due to a variety of arm issues. When healthy, the former third-round Draft pick has proven to be a quality starter, but staying on the mound has been his biggest challenge.
The Mariners are looking for pitching depth after releasing veterans Randy Wolf and Scott Baker earlier this week. With All-Star right-hander Hisashi Iwakuma sidelined until at least mid- to late April by a sprained finger tendon, and top young prospect Taijuan Walker just beginning to throw in Minor League outings after a sore shoulder slowed him in camp, Seattle was down to five healthy starting candidates.
Felix Hernandez is scheduled to make his seventh Opening Day start on Monday in Anaheim, and Erasmo Ramirez will follow on Tuesday. Manager Lloyd McClendon has yet to announce his other starters, but young left-hander James Paxton appears to be lined up to pitch the third game and rookie Roenis Elias has pitched well this spring and also is contending for a spot.
If he's ready, Young could compete with Blake Beavan for the fifth spot in the rotation. The Mariners have yet to announce a starter for their final Cactus League game Saturday against the Rockies.
Hernandez and Ramirez have already made their final spring starts. Paxton is pitching in a Minor League game Thursday, since Seattle is off. Elias will start Friday night against the Rockies in Scottsdale, Ariz.
Young passed his physical with the Mariners on Thursday. He started two games this spring with the Nationals, and most recently threw in relief on Saturday, when he tossed 2 1/3 scoreless innings, allowing one hit, no walks and three strikeouts against the Marlins.
Young is tied with Mariners Hall of Famer Randy Johnson for the second-tallest player in Major League history behind the 6-foot-11 Jon Rauch. Young earned a degree in politics from Princeton, where he played baseball and two seasons of basketball and won the Ivy League Rookie of the Year Award in both sports in 1999.