5. Darell Johnson: 1977-1980 – Record: 226-362 (.384)
Johnson had the second worst winning percentage in Mariners’ history, but checks in at fifth on this list. He was the first to manage the Mariners, which meant he led an expansion team and didn’t get to pick what he worked with. The Mariners did not see a winning season under his guide. The 1978 season was particularly bad, with Seattle finishing 56-104. He was fired before completing his fourth season with the team.