"It's been a little bit of a whirlwind," Ruffin said. "I'm just trying to settle it down a little. I knew this was a possibility when I saw there was a player to be named, I knew it could be anybody, so I kept myself mentally prepared."
Ruffin was drafted last year by Detroit as a first-round supplemental pick -- the 48th selection overall -- and appeared in two games for the Tigers earlier this season.
Ruffin was elevated immediately to Seattle's 25-man Major League roster. To make room, the Mariners designated left-handed reliever Aaron Laffey for assignment and will have 10 days to trade, release or outright his contract.
Ruffin joins rookies Josh Lueke, Dan Cortes and Tom Wilhelmsen in Seattle's bullpen, along with veterans Jamey Wright, Brandon League and Jeff Gray.
Wright actually played with Ruffin's dad, 11-year Major League pitcher Bruce Ruffin, in Colorado, as did Mariners manager Eric Wedge at a different point in time.
"Looks just like his old man," Wedge said. "He's a young kid with a good arm that is very accustomed to a bullpen role. He's been a late-inning guy whether in college or the short period of time in pro ball. In regard to where he'll be with us, I just told him to be ready.
"When it comes to these younger kids, we really don't have roles for them. We just want to continue to see them and they'll develop into roles."
Ruffin, a 6-foot, 185-pound Texan, has 19 saves and a 2.03 ERA in 44 games this season with Double-A Erie and Triple-A Toledo in the Tigers' farm system.
Seattle previously received outfielder Casper Wells and right-handed pitcher Charlie Furbush, both of whom are playing for the Mariners, as well as Double-A third base prospect Francisco Martinez.
At the time of the trade, Mariners general manager Jack Zduriencik said the club would also receive a "significant" player to be named later, with that player turning out to be the well-regarded Ruffin.
Because players can't be traded within the first year of signing their initial pro contract, Ruffin couldn't be included in the deal until now.
He's posted a 1.84 ERA with nine saves in 13 appearances with Toledo, with 17 strikeouts and six walks in 14 2/3 innings. Prior to that he struck out 43 batters in 34 innings in Erie, with a 2.12 ERA and 3-3 record in 31 games.
Ruffin pitched in two games for the Tigers in late July, with a 4.91 ER in 3 2/3 innings. The rookie allowed two solo home runs in a 1 2/3-innings debut at the White Sox, but bounced back three days later with two scoreless frames, giving up two hits and striking out two against the Angels.
"That did help, just getting into the [Major League] atmosphere a little," Ruffin said of his brief callup. "The first-time jitters are out of the way, now I'm just ready to go to work."
Wells and Furbush have already fit in well in Seattle. Wells hit home runs in four straight games going into Wednesday's series finale with Toronto, batting .341 (15-for-44) with 12 RBIs in his first 12 games for the Mariners.
Furbush is 2-1 with a 4.76 ERA in four appearances for Seattle and is coming off seven innings of one-run ball in his last start against the Red Sox.
Martinez, 20, has hit .276 in 15 games for Double-A Jackson, with one home run and 11 RBIs.