Despite his drop in form, Sinckler was later selected in England's squad for the 2019 Rugby World Cup. He was named in the starting line-up in all but one match, and scored his maiden test try in their quarter-final victory over Australia. The team's excellent form during their campaign saw them qualify for the final against South Africa; in the third minute, Sinckler made accidental contact with teammate Maro Itoje's elbow while attempting to tackle Makazole Mapimpi and was knocked out. After being helped on the field by the medical staff, he was helped off and ruled out for the rest of the match, in which they were defeated 32–12.