On December 3, 2018, the Phillies traded Crawford and Carlos Santana to the Seattle Mariners in exchange for Jean Segura, James Pazos and Juan Nicasio.[24] On March 13, 2019, the Mariners optioned Crawford to AAA Tacoma Rainiers. On May 10, 2019, the Mariners called up Crawford following an impressive stint in AAA, hitting a .319/.420/.457 slash line with 7 doubles, 3 home runs and 15 RBI and reaching base in all 31 games with the Rainiers. He made his Mariners debut on the same day against the Boston Red Sox at Fenway Park. Crawford’s first home run as a Mariner came off Michael Pineda against the Minnesota Twins on May 16, 2019. Crawford spent the remainder of the season as the starting shortstop for Seattle, hitting .226 with 7 home runs and 46 RBI in 93 games.
In 2020, Crawford batted .255/.336/.338 with two home runs, 24 RBIs and 33 runs scored in 53 games during the pandemic-shortened season. He was awarded the Gold Glove Award for the best defensive shortstop in the American League in 2020.
On June 19, 2021, Crawford hit his first career grand slam off of Tampa Bay Rays starting pitcher Josh Fleming.
