Walker will be the fourth starter in the rotation this season, the Tacoma News Tribune reports.
This was expected, but manager Scott Servais confirmed it Monday. Walker was shelled for six runs in his last spring start, but he's pitched pretty well overall with 16 strikeouts in 17 innings and two walks. If Walker takes the next step as the Mariners expect, he could have a breakout year after an inconsistent 2015.