Mariners Roster & Staff
Transactions
| Date | Transaction |
| 06/30/21 | Seattle Mariners activated LHP Marco Gonzales from the paternity list. |
| 06/30/21 | Seattle Mariners signed free agent RHP Franklin Van Gurp to a minor league contract. |
| 06/30/21 | Seattle Mariners optioned 2B Donovan Walton to Tacoma Rainiers. |
| 06/28/21 | Seattle Mariners sent RHP Erik Swanson on a rehab assignment to Tacoma Rainiers. |
| 06/28/21 | Seattle Mariners optioned RHP Robert Dugger to Tacoma Rainiers. |
| 06/28/21 | Seattle Mariners signed free agent C Eric Jones to a minor league contract. |
| 06/28/21 | Seattle Mariners signed free agent LHP Nate Fisher to a minor league contract. |
| 06/27/21 | Seattle Mariners placed LHP Marco Gonzales on the paternity list. |
| 06/27/21 | Seattle Mariners recalled RHP Yohan Ramirez from Tacoma Rainiers. |
| 06/27/21 | Seattle Mariners recalled RHP Robert Dugger from Tacoma Rainiers. |
| 06/25/21 | Seattle Mariners sent LHP Daniel Zamora outright to Tacoma Rainiers. |
| 06/24/21 | Seattle Mariners optioned RHP Vinny Nittoli to Tacoma Rainiers. |
| 06/24/21 | Seattle Mariners designated LHP Daniel Zamora for assignment. |
| 06/24/21 | Tampa Bay Rays traded 3B Wyatt Mathisen to Seattle Mariners for cash. |
| 06/24/21 | Seattle Mariners recalled RHP Keynan Middleton from Tacoma Rainiers. |
| 06/22/21 | Seattle Mariners claimed SS Jake Hager off waivers from Milwaukee Brewers. |
| 06/22/21 | Seattle Mariners optioned RHP Yohan Ramirez to Tacoma Rainiers. |
| 06/22/21 | Seattle Mariners recalled 2B Donovan Walton from Tacoma Rainiers. |
| 06/22/21 | Seattle Mariners placed 1B Evan White on the 60-day injured list. Left hip flexor strain. |
| 06/22/21 | Seattle Mariners optioned SS Jake Hager to Tacoma Rainiers. |
| 06/18/21 | Seattle Mariners recalled RHP Yohan Ramirez from Tacoma Rainiers. |
| 06/18/21 | Seattle Mariners placed RHP Justin Dunn on the 10-day injured list. Right shoulder inflammation. |
| 06/18/21 | Seattle Mariners optioned C Jose Godoy to Tacoma Rainiers. |
| 06/18/21 | Seattle Mariners placed CF Kyle Lewis on the 60-day injured list. Right meniscus tear. |
| 06/18/21 | Seattle Mariners selected the contract of RHP Vinny Nittoli from Tacoma Rainiers. |
| 06/17/21 | Seattle Mariners signed free agent 2B Alen Hanson to a minor league contract. |
| 06/14/21 | Seattle Mariners recalled C Luis Torrens, and from Tacoma Rainiers. |
| 06/14/21 | Seattle Mariners optioned RHP Yohan Ramirez to Tacoma Rainiers. |
| 06/14/21 | Seattle Mariners traded RHP Yacksel Rios to Boston Red Sox for cash. |
| 06/14/21 | Seattle Mariners traded SS Andres Mesa to Texas Rangers. |
| 06/13/21 | Los Angeles Angels claimed 2B Jack Mayfield off waivers from Seattle Mariners. |
| 06/12/21 | Seattle Mariners optioned LF Dillon Thomas to Tacoma Rainiers. |
| 06/12/21 | Seattle Mariners sent C Jacob Nottingham outright to Tacoma Rainiers. |
| 06/12/21 | Seattle Mariners optioned 2B Donovan Walton to Tacoma Rainiers. |
| 06/12/21 | Seattle Mariners activated 1B Dylan Moore. |
| 06/12/21 | Seattle Mariners recalled RHP Yohan Ramirez from Tacoma Rainiers. |
| 06/11/21 | Seattle Mariners activated RHP Kendall Graveman. |
| 06/11/21 | Seattle Mariners designated RHP Yacksel Rios for assignment. |
| 06/11/21 | Seattle Mariners optioned RHP Keynan Middleton to Tacoma Rainiers. |
| 06/11/21 | Seattle Mariners activated RHP Justin Dunn from the 10-day injured list. |
| 06/10/21 | Seattle Mariners designated 2B Jack Mayfield for assignment. |
| 06/10/21 | Cleveland Indians traded DH Jake Bauers to Seattle Mariners for Player To Be Named Later. |
| 06/10/21 | Seattle Mariners sent 1B Evan White on a rehab assignment to Tacoma Rainiers. |
| 06/08/21 | Seattle Mariners designated C Jacob Nottingham for assignment. |
| 06/08/21 | Seattle Mariners sent RHP Kendall Graveman on a rehab assignment to Tacoma Rainiers. |
| 06/08/21 | Seattle Mariners selected the contract of LF Dillon Thomas from Tacoma Rainiers. |
| 06/07/21 | Seattle Mariners optioned OF Jarred Kelenic to Tacoma Rainiers. |
| 06/07/21 | Seattle Mariners activated 2B Shed Long Jr. |
| 06/07/21 | Seattle Mariners sent 1B Dylan Moore on a rehab assignment to Tacoma Rainiers. |
| 06/07/21 | Seattle Mariners placed 2B Sam Haggerty on the 60-day injured list. Right shoulder inflammation. |
| 06/05/21 | Seattle Mariners activated RHP Drew Steckenrider from the 10-day injured list. |
| 06/05/21 | Seattle Mariners optioned RHP Robert Dugger to Tacoma Rainiers. |
| 06/05/21 | Seattle Mariners optioned LHP Daniel Zamora to Tacoma Rainiers. |
| 06/05/21 | Seattle Mariners selected the contract of RHP Yacksel Rios from Tacoma Rainiers. |
| 06/04/21 | Tampa Bay Rays traded RHP Yacksel Rios to Seattle Mariners for cash. |
| 06/03/21 | Seattle Mariners signed free agent SS Zach Vincej to a minor league contract. |
| 06/02/21 | Seattle Mariners signed free agent LHP Steven Moyers to a minor league contract. |
| 06/02/21 | Seattle Mariners sent 3B Eric Campbell outright to Tacoma Rainiers. |
| 06/02/21 | Seattle Mariners placed RHP Justin Dunn on the 10-day injured list. Right shoulder inflammation. |
| 06/02/21 | Seattle Mariners recalled RHP Robert Dugger from Tacoma Rainiers. |
| 06/01/21 | Seattle Mariners optioned RHP Robert Dugger to Tacoma Rainiers. |
| 06/01/21 | New York Mets claimed 3B Travis Blankenhorn off waivers from Seattle Mariners. |
| 06/01/21 | Seattle Mariners placed CF Kyle Lewis on the 10-day injured list. Right knee discomfort. |
| 06/01/21 | Seattle Mariners activated LHP Marco Gonzales from the 10-day injured list. |
| 06/01/21 | Seattle Mariners recalled LF Taylor Trammell from Tacoma Rainiers. |
| 06/01/21 | Seattle Mariners recalled 3B Travis Blankenhorn from Tacoma Rainiers. |