The D-backs got younger and picked up extra years of club control in the deal, banking on the upside of Walker and Marte while dealing Segura on the heels of a career year when he hit .319 with 20 homers and 33 stolen bases.
Walker is the headliner in the deal, a 24-year-old who has outstanding stuff that he is still working to harness on a consistent basis. He has pitched in parts of four seasons for the Mariners going 22-22 with a 4.18 ERA in 65 games (62 starts). Haniger, who was named Arizona's 2016 Minor League player of the Year, now ranks as Seattle's No. 14 prospect, according to MLBPipeline.com. The 25-year-old made his Major League debut in 2016, hitting .229 with five home runs and 17 RBIs in 34 games, after finishing with a .321 average, 25 homers and 94 RBIs between Double-A Mobile and Triple-A Reno.
"Obviously, Jean is a great fit for them and was for us, but in order for us to get a starting pitcher the caliber of Taijuan, we felt like this was the opportunity we had to take, given the market," Hazen said. "It takes a lot of starting pitching to get through the season. Depth in your rotation and talent in your rotation is critical to being successful."
The D-backs were last in the Majors in ERA last season, and improving the staff was a top priority for Hazen.
Walker also comes with four years left of club control. MLBTraderumors.com projects him to earn $2.8 million in 2017 as a "Super Two" player.
Hate to see guy go but that's part of the business. @tai_walker let's get it bro!!!
"It's not one of those guys that you're able to acquire all the time, with the state of the game now with pitching and the premium, especially on starting pitching," Hazen said. "We felt like this was an opportunity we needed to take."
Marte, 23, appeared in 57 games for the Mariners in 2015 before becoming their primary shortstop last season, slashing .259/.287/.323 in 466 plate appearances. He has also played second base and in the outfield.
"We think he can play anywhere, really," Hazen said. "We just think we love the athleticism and the all-around player. When he was in the Minor Leagues, the way he controlled the strike zone, he got up to the big leagues quick as a 22-year-old, and we think there's definitely some upside in the bat and the defensive ability and the speed and the athleticism. All around, we feel he adds quite a bit to our club."
Segura had two years of club control left and is projected to make a little more than $7 million in arbitration this winter. His departure opens up playing time in the middle of the diamond, and the D-backs certainly have plenty of depth there.
Segura, who turns 27 in March, gives the Mariners their much-coveted shortstop to pair with second baseman Robinson Cano -- and one who quietly enjoyed one of the better offensive performances in the National League last season. Segura hit .319 with 20 home runs and 64 RBIs in 153 games for Arizona, adding 33 steals and posting an .867 OPS. His 203 hits ranked first in the National League.
"We just feel at this point, this trade made more sense with where our roster is," Seattle general manager Jerry Dipoto said, "and Jean Segura fit this club about as well as any player we were looking at in the trade market."
Chris Owings, like Marte, can play both short and second. Shortstop Nick Ahmed is expected to be ready for the start of Spring Training after suffering a hip injury last season. Phil Gosselin can play second and third, as can Brandon Drury.
Drury showed his potential with the bat last season, but he is blocked at third by Jake Lamb, and the outfield doesn't seem like a long-term fit for him. So moving Segura could lead to Drury getting more at-bats, depending on whether Ahmed, Owings or Marte plays shortstop.
"There's going to be a lot of competition coming into Spring Training," Hazen said, "and I think that's a good thing for our club, a good thing for our players."
Haniger was the D-backs' Minor League Player of the Year in 2016, and he made his big league debut in September, showing he can play an above-average center field.
Curtis jumped all the way from Class A Advanced Visalia to the big leagues when the D-backs needed left-handed help in the bullpen.
Steve Gilbert has covered the D-backs for MLB.com since 2001. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.