Seattle general manager Jack Zduriencik said the player to be named is a "significant" prospect that will be chosen from a pool of three Minor Leaguers the team is still evaluating and will be determined in the next three weeks.
Furbush and Wells will join the Mariners' 25-man roster and be active for Sunday's series finale against Tampa Bay. Martinez will report to Double-A Jackson in the Southern League.
"What we did is acquire players we're going to have for a long time," Zduriencik said. "When you start looking at controlling younger players for five-six years, that's pretty good. We've said we want to accumulate talent and stockpile players who'll be here for a long time and players that fit needs we have.
"In this trade we'll get immediate help in a couple guys coming here right to the big leagues and a couple very good prospects."
Fister has been the Mariners' hard-luck story this season, with the lowest run-support average in the American League resulting in a 3-12 record despite his 3.33 ERA. Seattle totaled just 10 runs in his 12 losses.
"Obviously it's a whirlwind of emotions," Fister said, "but I'm excited to get over there and be a Tiger."
Pauley developed into a quality reliever this season, his first full-time stint out of the bullpen and has a 2.15 ERA in 39 appearances.
Manager Eric Wedge said both Pauley and Fister had stepped up strong this season and deserved the opportunity to compete on a playoff push with the Tigers, who currently lead the AL Central, but said this was the type of deal that should benefit the Mariners in the long run.
"There are always x-factors involved," said Wedge, "but the fact of the matter is that we felt like we could make a deal that would help us be better now and into the future, and that's what we did."
Martinez, 20, played in the Futures Game this month and is a big third baseman with power potential. He's hitting .282 with seven home runs in 91 games at Double-A Erie. Zduriencik said Martinez is one of the youngest Double-A players in the Minors and was rated one of the Tigers' top prospects coming into the year.
"Our people say he's got great work habits, a kid with a lot of desire and the future is ahead of him," Zduriencik said. "We think he can be an everyday player -- and a significant one."
Wells, 26, can play all three outfield spots and is regarded as a very good defender and a right-handed hitter with some power potential as well who'll get an immediate shot with Seattle.
Wells is batting .257 with four home runs, 12 RBIs and a .323 on-base percentage in 64 games this season with the Tigers, his second in the Majors. He hit .323 with four home runs and 17 RBIs last year in 36 games, giving him a two-year average of .286 in 100 games.
The 6-foot-2, 210-pound Wells was a 14th-round Draft pick by the Tigers in 2005. He becomes arbitration eligible in 2013 and won't be eligible for free agency until '16.
"There's no question we're offensively challenged," Zduriencik said. "One of the things we tried to do from the very beginning is acquire a right-handed bat. We got a guy who has extra-base power, he's athletic and can play all three outfield spots."
Wedge said Wells would fit into the left-field mix with rookies Mike Carp and Greg Halman and could play center and right as well.
Furbush, a 25-year-old rookie and a fourth-round pick in 2007, is 1-3 with a 3.62 ERA in 32 1/3 innings and 17 appearances, two of which were starts.
Zduriencik said Furbush will be given a shot as a starter with the Mariners, though Wedge noted he'd need to be built up before getting tossed totally into the rotation picture.
With the Trade Deadline still looming Sunday at 1 p.m. PT, it's possible the Mariners could still shake things up further, so nothing is set in stone at this point.
Zduriencik preferred not to break up his pitching depth, but rookie Blake Beavan impressed the club in the past weeks in place of Erik Bedard, as he went 1-2 with a 3.04 ERA in four starts. Beavan was not sent down when Bedard came off the 15-day disabled list Friday, so he'll be able to slide into Fister's starting spot Monday against the A's.
An emotional Pauley said the move blindsided him a bit, even though he'd heard rumors.
"My agent called me this morning [at] about 8 [a.m.] and I knew that probably wasn't a good sign," Pauley said. "I've gone through it before, but it's always tough. This is a good group of guys.
"A lot of things happened this year that probably not too many people expected. It's turned out for the best this year, [and] everything has gone well. I guess it's just a stepping-stone in my career."
Fister acknowledged that "the ball didn't roll our way all the time this year," but it would be difficult to say goodbye to the players he's competed with for the past three seasons.
"I'm excited for the new adventure, but sad to leave this clubhouse and the Seattle Mariners," Fister said. "It's been a great experience. The teammates we have here, it's one in a million. We've got the brotherhood and camaraderie that any team desires. That's the hard part to leave."