The Yankees confirmed Monday they dealt left-handed pitcher Justus Sheffield, right-handed pitcher Erik Swanson and outfielder Dom Thompson-Williams in exchange for Paxton.
Yahoo Sports' Jeff Passan first reported the deal.
Mariners shortstop Jean Segura was mentioned in trade talks before the Yankees focused on Paxton, according to Jon Morosi of Fox Sports, adding that would have "all but eliminated" New York as a destination for Manny Machado.
Passan reported Nov. 6 that the Mariners were considering a "full-fledged teardown" if the trade market was strong.
Seattle general manager Jerry Dipoto downplayed those rumors, telling MLB.com's Greg Johns and Maria Guardado the team was still hoping to compete for a playoff spot:
"We know what the [Houston] Astros, [Boston] Red Sox, [Oakland] A's, Yankees and [Cleveland] Indians look like. We don't want to be a perpetual competitor for the second Wild Card. We want to build a championship roster. If that means in 2019 we field as competitive a team as we can while earmarking and gathering talent, we're not looking to rip our club down. We're just too talented to do that."
With Paxton under team control for two more seasons, Seattle's best long-term plan was to at least explore trade possibilities. Despite a 3.52 ERA and 481 strikeouts in 417.1 innings since 2016, there are red flags that it might not last.
Injuries have landed Paxton on the disabled list in each of his first six MLB seasons, including two different stints in 2018. He had lower-back inflammation in July and a forearm contusion in August.
Paxton is coming off his most successful season. The southpaw set career highs with 28 starts, 160.1 innings and 208 strikeouts to help the Mariners post their best record (89-73) since 2003.
The Yankees came into this offseason knowing they needed to add at least one impact starting pitcher. They did re-sign CC Sabathia to a one-year deal, but the 38-year-old is more of a depth starter for 2019.
Now that the Yankees have added Paxton to the mix, they head into 2019 with a quartet of starters that also includes Masahiro Tanaka and Luis Severino.
Even with some possible issues, Paxton gives New York a potential impact arm who can rack up huge strikeout totals alongside Severino (220 strikeouts in 190.1 innings last season) and Tanaka (159 strikeouts in 156 innings) as the team tries to end the Boston Red Sox's three-year run atop the American League East.