After starting a couple of games after being activated, Graveman was placed again on the disabled list on May 29 due to shoulder soreness. On March 20, Graveman was announced as the 2018 opening day starter for the second consecutive year. After starting the season 0–5 with an 8.89 ERA, Graveman was demoted to Triple-A on April 26. Graveman underwent Tommy John surgery on July 24, 2018. He was non-tendered by the Athletics on November 30, 2018, and became a free agent. Graveman signed a one-year contract with an option for the 2020 season with the Chicago Cubs on December 23, 2018. He became a free agent after the season. On November 26, 2019, Graveman signed a one-year contract with the Seattle Mariners. Graveman is a sinkerballer, throwing his sinker between 91 and 96 MPH. He also throws a cutter, a slider, and a change-up.