Swihart was converted into a utility player for 2018; he played first base, third base, catcher, and left field during spring training. In mid-May, his agent asked the Red Sox to trade Swihart, given his limited playing time with the team. At the time, Swihart was hitting .138 (4-for-29) in 32 plate appearances, having played games at catcher, first base, left field, and designated hitter. Swihart was placed on the disabled list on August 3, with a right hamstring strain. To that point in the season, he had appeared in 51 games, batting .226 with one home run and six RBIs. He returned to the active roster on August 14. Swihart played throughout the season as a bench player, appearing in 82 games and batting .229/.285/.328 with three home runs. In the postseason, Swihart played two innings in the outfield and caught one inning, going 0-for-3 at the plate, as the Red Sox won the World Series in five games over the Los Angeles Dodgers.