In the pandemic-shortened 2020 regular season, Gonsolin went 2–2 with a 2.31 ERA, in nine games (eight starts) during which he struck out 46 batters in innings. In the postseason, he made two appearances in the NLCS, starting game two and appearing in relief in game seven. He pitched a total of 6 innings, allowing seven runs and picking up the loss in game two. In the World Series, he was selected by Dodgers manager Dave Roberts to start Game 2, on two days rest, against the Tampa Bay Rays. He only pitched innings in the game and allowed one earned run on one hit and one walk as he was awarded the loss in the game. He also got the start in Game 6 and this time pitched innings while allowing one run on three hits and two walks; however, the Dodgers came from behind to win that game and clinch the championship. Gonsolin received eleven votes in 2020 National League Rookie of the Year voting, finishing in fourth place. On October 26, 2020, Baseball America named Gonsolin its 2020 Rookie of the Year.
