| | P | Sent to Minors (The Seattle Mariners sent LHP Justus Sheffield outright to the minors.) |
| | RF | Sent to Minors (The Seattle Mariners sent OF Alberto Rodriguez to the minors.) |
| | DH | Signed (The Seattle Mariners signed INF Robbie Tenerowicz to a minor league contract.) |
| | DH | Signed (The Seattle Mariners signed INF Robbie Tenerowicz to a minor league contract.) |
| | 3B | Signed (The Seattle Mariners signed INF Jason Vosler to a minor league contract.) |
| | P | Signed to a Minor League Contract (Signed) |
| | P | Drafted Via Rule 5 (Signed) |
| | SS | Drafted Via Rule 5 (Minor-league phase) |
| | P | Signed to a Minor League Contract (Signed) |
| | 3B | Traded (with OF Jesse Winker for 2B Kolten Wong) To |
| | LF | Traded (with INF Abraham Toro for 2B Kolten Wong) To |
| | 2B | Traded (for OF Jesse Winker and INF Abraham Toro) From |
| | P | Signed as Free Agent (one-year contract) |
| | P | Signed to a Minor League Contract (Signed) |
| | C | Free Agent - No Contract Offer (non-tendered) |
| | P | Free Agent - No Contract Offer (non-tendered) |
| | C | Free Agent - No Contract Offer (non-tendered) |
| | LF | Traded (for OF Kyle Lewis) From |
| | CF | Traded (for C/OF Cooper Hummel) To |
| | P | Traded (for OF Teoscar Hernandez, 3-player deal) To |
| | P | Traded (w/P Adam Macko for OF Teoscar Hernandez) To |
| | RF | Traded (for RHP Erik Swanson & LHP Adam Macko) From |
| | RP | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | SP | Declared Free Agency (Signed) |
| | 3B | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | SS | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | SS | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | 2B | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | 3B | Declared Free Agency (Signed) |
| | CF | Declared Free Agency (Signed) |
| | 2B | Declared Free Agency (Signed) |
| | P | Refused Minor League Assignment - Free Agent (Signed) |
| | P | Refused Minor League Assignment - Free Agent (Signed) |
| | P | Refused Minor League Assignment - Free Agent (Signed) |
| | P | Outrighted to Minors (Signed) |
| | P | Acquired Off Waivers (Signed) From |
| | P | Traded (for cash considerations) From |
| | P | Outrighted to Minors (Signed) |
| | P | Purchased From Minors (Signed) |
| | RF | Declared Free Agency (Signed) |
| | 1B | Declared Free Agency (Signed) |
| | C | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | 2B | Declared Free Agency (Signed) |
| | 3B | Outrighted to Minors (Signed) |
| | CF | Outrighted to Minors (Signed) |
| | P | Acquired Off Waivers (Signed) From |
| | CF | Designated for Assignment (Signed) |
| | LF | Removed From 10-Day IL (Neck injury) |
| | RF | Removed From 10-Day IL (Left groin strain) |
| | P | Declared Free Agency (Signed) |
| | RF | Declared Free Agency (Signed) |
| | P | Declared Free Agency (Signed) |
| | P | Called Up from Minors (Signed) |
| | CF | Called Up from Minors (Signed) |
| | RF | Called Up from Minors (Signed) |
| | P | Called Up from Minors (Signed) |
| | 1B | Called Up from Minors (Signed) |
| | P | Called Up from Minors (Signed) |
| | C | Called Up from Minors (Signed) |
| | CF | Called Up from Minors (Signed) |
| | 3B | Called Up from Minors (Signed) |
| | LF | Placed on 10-Day IL (Neck injury) |
| | RF | Called Up from Minors (Signed) |
| | P | Called Up from Minors (recalled as 29th roster player) |
| | 3B | Called Up from Minors (Signed) |
| | P | Return of 27th man (Signed) |
| | RF | Placed on 10-Day IL (Left groin strain) |
| | C | Sent to Minors (Signed) |
| | 3B | Sent to Minors (Signed) |
| | P | Outrighted to Minors (Signed) |
| | CF | Removed From 10-Day IL (Lower back strain) |
| | C | Reinstated from Paternity Leave List (Signed) |
| | C | Purchased From Minors (Signed) |
| | C | Placed on Paternity Leave List (Signed) |
| | P | Designated for Assignment (Signed) |
| | 3B | Removed From 10-Day IL (Fractured right index finger) |
| | RF | Sent to Minors (Signed) |
| | 3B | Refused Minor League Assignment - Free Agent (Signed) |
| | 3B | Outrighted to Minors (Signed) |
| | P | Signed (five-year contract extension) |
| | CF | Placed on 10-Day IL (Lower back strain) |
| | RF | Called Up from Minors (Signed) |
| | 3B | Designated for Assignment (Signed) |
| | RF | Sent to Minors (Signed) |
| | C | Purchased From Minors (Signed) |
| | LF | Called Up from Minors (Signed) |
| | 3B | Placed on 10-Day IL (Fractured right index finger) |
| | RF | Removed From 10-Day IL (Right oblique strain) |
| | RF | Recalled From Minors Rehab (Signed) |
| | RF | Sent to Minors for Rehabilitation (Signed) |
| | P | Recalled From Minors Rehab (Signed) |
| | RF | Called Up from Minors (Signed) |
| | RF | Placed on 10-Day IL (Right oblique strain) |
| | 3B | Called Up from Minors (Signed) |
| | 1B | Recalled From Minors Rehab (Signed) |
| | 1B | Sent to Minors (Signed) |
| | P | Released (Signed) |
| | P | Signed to a Minor League Contract (Signed) |
| | C | Outrighted to Minors (Signed) |
| | P | Refused Minor League Assignment - Free Agent (Signed) |
| | RF | Sent to Minors (Signed) |
| | RF | Removed From 10-Day IL (COVID-19 injured list (positive test)) |
| | RF | Recalled From Minors Rehab (Signed) |
| | P | Sent to Minors for Rehabilitation (Signed) |
| | P | Designated for Assignment (Signed) |
| | P | Recalled From Minors Rehab (Signed) |
| | CF | Removed From 10-Day IL (Right wrist contusion) |
| | RF | Released (Signed) |
| | C | Designated for Assignment (Signed) |
| | LF | Sent to Minors (Signed) |
| | C | Removed From 10-Day IL (Right oblique strain) |
| | P | Recalled From Minors Rehab (Signed) |
| | CF | Sent to Minors (Signed) |
| | P | Sent to Minors (Signed) |
| | RF | Removed From 10-Day IL (Back spasms) |
| | P | Signed to a Minor League Contract (Signed) |
| | 1B | Sent to Minors for Rehabilitation (Signed) |
| | LF | Refused Minor League Assignment - Free Agent (Signed) |
| | LF | Outrighted to Minors (Signed) |
| | P | Called Up from Minors (Signed) |
| | 3B | Acquired Off Waivers (Signed) To |
| | P | Sent to Minors for Rehabilitation (Signed) |
| | P | Acquired Off Waivers (Signed) To |
| | RF | Recalled From Minors Rehab (Signed) |
| | 3B | Sent to Minors (Signed) |
| | P | Return of 27th man (Signed) |
| | P | Called Up from Minors (recalled as 27th roster player) |
| | CF | Acquired Off Waivers (Signed) From |
| | 3B | Designated for Assignment (Signed) |
| | CF | Sent to Minors (Signed) |
| | LF | Designated for Assignment (Signed) |
| | P | Cleared Waivers and Became a Free Agent (Signed) |
| | CF | Outrighted to Minors (Signed) |
| | 3B | Released (Signed) |
| | RF | Outrighted to Minors (Signed) |
| | P | Released (Signed) |
| | P | Sent to Minors for Rehabilitation (Signed) |
| | P | Traded (with C Curt Casali, four-player deal) From |
| | 3B | Traded (for future considerations) From |
| | C | Traded (with LHP Matthew Boyd, four-player deal) From |
| | 3B | Sent to Minors (Signed) |
| | P | Designated for Assignment (Signed) |
| | CF | Designated for Assignment (Signed) |
| | LF | Acquired Off Waivers (Signed) From |
| | P | Traded (for cash considerations) To |
| | 2B | Signed to a Minor League Contract (Signed) |
| | RF | Sent to Minors for Rehabilitation (Signed) |
| | RF | Placed on 10-Day IL (Back spasms) |
| | CF | Placed on 10-Day IL (Right wrist contusion) |
| | P | Sent to Minors (Signed) |
| | P | Designated for Assignment (Signed) |
| | LF | Called Up from Minors (Signed) |
| | CF | Called Up from Minors (Signed) |
| | RF | Designated for Assignment (Signed) |
| | P | Purchased From Minors (Signed) |
| | P | Sent to Minors (Signed) |
| | P | Acquired Off Waivers (Signed) From |
| | P | Traded (for RHP Luis Castillo, five-player deal) To |
| | SS | Traded (for RHP Luis Castillo, five-player deal) To |
| | SS | Traded (for RHP Luis Castillo, five-player deal) To |
| | P | Traded (for RHP Andrew Moore, five-player deal) From |
| | P | Called Up from Minors (Signed) |
| | P | Called Up from Minors (Signed) |
| | P | Sent to Minors (Signed) |
| | CF | Removed from 7-Day IL (Concussion) |
| | CF | Recalled From Minors Rehab (Signed) |
| | P | Signed to a Minor League Contract (Signed) |
| | LF | Declared Free Agency (refused option) |
| | LF | Sent to Minors (Signed) |
| | RF | Sent to Minors for Rehabilitation (Signed) |
| | RF | Retired (Signed) |
| | P | Released (Signed) |
| | P | Refused Minor League Assignment - Free Agent (Signed) |
| | 3B | Sent to Minors (Signed) |
| | 1B | Reinstated from Bereavement/Family Medical Emergency List (Signed) |
| | 3B | Called Up from Minors (Signed) |
| | 1B | Placed on Bereavement/Family Medical Emergency List (Signed) |
| | P | Called Up from Minors (recalled as 27th roster player) |
| | C | Cleared Waivers and Became a Free Agent (Signed) |
| | CF | Reinstated From League Suspension (Signed) |
| | P | Return of 27th man (Signed) |
| | CF | Starting to Serve Suspension (Signed) |
| | LF | Reinstated From League Suspension (Signed) |
| | C | Released (Signed) |
| | P | Designated for Assignment (Signed) |
| | P | Reinstated from Paternity Leave List (Signed) |
| | P | Sent to Minors (Signed) |
| | C | Removed From 10-Day IL (Left shoulder injury) |
| | C | Recalled From Minors Rehab (Signed) |
| | C | Designated for Assignment (Signed) |
| | P | Placed on Paternity Leave List (Signed) |
| | P | Called Up from Minors (Signed) |
| | P | Called Up from Minors (Signed) |
| | P | Purchased From Minors (Signed) |
| | C | Sent to Minors for Rehabilitation (Signed) |
| | 1B | Removed From 10-Day IL (Left flexor strain) |
| | RF | Sent to Minors (Signed) |
| | LF | Starting to Serve Suspension (Signed) |
| | SS | Reinstated From League Suspension (Signed) |
| | CF | Sent to Minors for Rehabilitation (Signed) |
| | SS | Starting to Serve Suspension (Signed) |
| | C | Transferred to 60-Day IL (Left shoulder surgery - out for season) |
| | RF | Placed on 10-Day IL (COVID-19 injured list (positive test)) |
| | 3B | Sent to Minors (Signed) |
| | RF | Called Up from Minors (Signed) |
| | RF | Purchased From Minors (Signed) |
| | P | Signed to a Minor League Contract (Signed) |
| | 3B | Sent to Minors (Signed) |
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