Ramirez, 25, was obtained by Seattle along with outfielder Ramon Flores from the Yankees in a trade for Dustin Ackley on July 31 and went 1-0 with an 11.57 ERA in five appearances in September. Flores was dealt to the Brewers last month for infielder Luis Sardinas.
Ramirez, who is out of Minor League options, had an 8.66 ERA in 16 relief appearances over the past two seasons with the Yankees and Mariners. He was 3-0 with 10 saves and a 2.90 ERA in 32 relief appearances for the Yankees' Triple-A Scranton/Wilkes-Barre club last year and 3-1 with a 9.00 ERA in nine outings for Seattle's Triple-A Tacoma.
The Mariners' 40-man roster is now at 39. The trade is the sixth made by new general manager Jerry Dipoto in the past month.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.