 Promoted to Seattle for the first time in July 2007, he struck out the first batter he faced, former Mariners' star Ken Griffey, Jr.. Rowland-Smith began 2008 as a relief pitcher for the Mariners but was sent to the minor leagues briefly in July to work on becoming a starting pitcher.He rejoined the team in August and remained in their starting rotation the rest of the year.In 2009, he made one start for the Mariners at the beginning of the year before going on the disabled list with triceps tendinitis.