Gran Turismo Wiki
"Claim victory through sheer finesse, or by perfectly tuning your car. Take on a variety of races using the cars you've obtained."
―In-game description (while selecting a league)

GT League's menu.

GT League is a game mode that was added in the Campaign section of Gran Turismo Sport as part of update 1.10, released on December 22, 2017. Similarly to the Gran Turismo Mode of previous games, this game mode includes several series of races that have appeared in past GT titles such as Sunday Cup, Clubman Cup, FF Challenge, FR Challenge, Mazda Roadsters Cup and more.

The events in GT League mode are divided in four categories. At the start of the game, only the Beginner category can be accessed, while the Amateur, Professional and Endurance categories can be accessed upon reaching Level 10, Level 20 and Level 30, respectively. There are a total of 301 races (46 events) in GT League. Due to continuously updating nature of GT League, there are no prize cars for completing every race in a GT League event, nor there are prize cars for completing all GT League events.

The music for this mode uses the album version of Gran Turismo 2's Arcade Mode menu music, "Windroad" by Isamu Ohira. All events in GT League feature rolling starts; there is an unused Gran Turismo 3: A-Spec race start music hidden in the files, which would have been used if there are grid start events.[1]