At the start of the 2005–06 free agent cycle, Lawton had eight teams that he would sign with. Two teams were intermediately not interested. The Seattle Mariners, which were one of the teams Lawton wanted to join, were wary of taking Lawton because of his drug suspension, but eventually signed him. The deal was made official on December 23, 2005. His contract was a one-year major league contract worth US$400,000, with more than US$1 million in possible incentives. It also had a no-trade clause. During spring training in 2006, the Mariners allowed Lawton and teammate Eddie Guardado leave camp to attend the funeral services for their former teammate Kirby Puckett. Lawton returned from his suspension on April 12. After activating him on the roster, the Mariners designated catcher Guillermo Quiróz for assignment. Lawton gave Mariners officials the permission required to release him, saying that "I went to them in a friendly manner and just said 'Hey, I'll be the guy you can send out' if they felt the need". Lawton was designated for assignment on May 20. Mariners general manager Bill Bavasi added Mike Morse to the major league roster in Lawton's place. With the Mariners that season, Lawton batted .259 with five runs scored, seven hits, and one RBI in 11 games played.