The club added Lynn to the 40 man roster and activated him on June 2, 2011. He made his MLB debut that night at Busch Stadium against the San Francisco Giants. In innings in the regular season with the Cardinals, Lynn notched 40 strikeouts while allowing 25 hits and 11 walks. A pulled flank muscle in August prevented him from appearing in a game until a surprise appearance in the postseason. On October 10, Lynn was awarded the win after throwing exactly one pitch in Game 2 of the National League Championship Series (NLCS) against the Milwaukee Brewers. In the World Series, Lynn gave up back-to-back home runs in the top of the seventh to Adrián Beltré and Nelson Cruz. However, he won the World Series with the Cardinals, making a total of 10 appearances during the postseason after appearing in just 18 games during the 2011 regular season.