Ellis made his MLB debut in June 1968, beginning as a relief pitcher, but the Pirates moved Ellis into the starting rotation later that season and he started 10 games. Ellis pitched his first complete game in September. He had a 6–5 win-loss record with a 2.51 ERA with the Pirates in 1968. In 1969, Ellis made the team's starting rotation for Opening Day. The struggles of Steve Blass kept Ellis in the starting rotation, as Blass was moved to the bullpen.