The Mariners activated Swanson (groin) from the 10-day injured list Wednesday, Ryan Divish of The Seattle Times reports.
The righty made two rehab appearances with Triple-A Tacoma, allowing a solo home run and striking out one in two innings. Before a right groin strain sent Swanson to the IL on May 29, he posted a 0.69 ERA with 14 strikeouts and six walks in 13 innings. He made nine appearances, two of which were starts.