News of the impending four-player swap initially leaked out eight days ago, but Montero, 22, had travel issues getting out of his native Venezuela last week, and then was further delayed by a snow storm that hit Seattle. Until players are medically cleared, the Mariners don't make trade announcements.
Once the deal is consummated, Montero, rated the No. 1 catching prospect by MLB.com last week, will come to Seattle, along with right-handed pitcher Hector Noesi, 24.
In return, the Yankees will receive Pineda -- a late addition to the American League All-Star team last year as a rookie -- along with Minor League pitcher Jose Campos, 19.
Montero hit .328 with four home runs and 12 RBIs in 61 at-bats after a late-season promotion by the Yankees. At 6-foot-3, 225 pounds, he figures to split time at catcher and designated hitter for the Mariners and provide a middle-of-the-order bat for an offense that has finished last in the American League in scoring for three straight years.
Noesi pitched 30 games for the Yankees last season -- including two starts -- while posting a 2-2 record with a 4.47 ERA. He is expected to challenge for a spot in the Mariners' rotation, which now includes Felix Hernandez, Jason Vargas, Japanese free-agent signee Hisashi Iwakuma and 2011 rookies Blake Beavan and Charlie Furbush.
Pineda, 23, led all AL rookies in strikeouts with 173 in 171 innings last year, while walking just 55. He posted the lowest WHIP (1.10) and second-lowest opponent's batting average (.211) and quality starts (19) among AL rookies.
The Yankees also will receive Campos, a young right-hander who went 5-5 with a 2.32 ERA for Class A Everett last year.