Hembree started the season as a member of the 2018 Red Sox, in his usual role as a member of Boston's bullpen. He finished 4–1 with a 4.10 ERA in 67 appearances, striking out 76 batters in 60 innings. Hembree was initially not included on Boston's postseason roster, but was added for the ALDS and beyond due to an injury to Steven Wright. Hembree made four appearances in the postseason, allowing no earned runs in innings, as Boston won the World Series over the Los Angeles Dodgers.