The Seattle Mariners began play as an expansion team in Major League Baseball in 1977.

Quick answer

  • The Mariners were founded and enfranchised in 1977 as an American League expansion team.
  • They played their first season in 1977 , with home games in the Kingdome in Seattle.

A bit of story

  • The franchise was created after Seattle and Washington officials sued the American League over the loss of the earlier Seattle Pilots; part of the settlement was a promise of a new team starting in 1977.
  • The name “Mariners” was chosen in 1976 through a fan contest, reflecting Seattle’s maritime ties, just before the club took the field for that inaugural 1977 season.

TL;DR: When people ask “when did the Mariners start,” it refers to their MLB debut as a franchise in 1977.

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