Byrnes was released by the Mariners on May 2, 2010 after batting .094 with 3 hits in 32 at-bats, 1 run scored, 2 doubles, 9 strikeouts, and 6 bases on balls in 15 games on the season with Seattle. In a press release by the Mariners, general manager Jack Zduriencik said that, "Eric Byrnes is a tremendous competitor and a credit to baseball. We wish him only the best and expect him to land on his feet." This ended a disappointing stint with the Mariners.