On July 24, 2020, Marmolejos made his MLB debut on Opening Day, going hitless over 3 at-bats against the Houston Astros. Marmolejos finished the 2020 season hitting .206 with 6 home runs and 18 RBI. Marmolejos hit .139 with 3 home runs and 9 RBI in 31 games for the Mariners in 2021 before being designated for assignment on May 20, 2021. He was outrighted to the Triple-A Tacoma Rainiers on May 23. After having a great stint with Triple-A Tacoma, hitting .360 with 23 home runs and 71 RBI's through 72 games, his contract was re-selected by the Mariners on August 30, 2021.
