Brentford initially played amateur football before they entered the London League in 1896 and finished as runners-up of the Second Division and then the First Division to win election into the Southern League in 1898. They won the Southern League Second Division in 1900–01 and were elected into the Football League in 1920. Brentford won the Third Division South title in 1932–33 and the Second Division title in 1934–35. They spent five seasons in the First Division, reaching a peak of fifth in 1935–36, before three relegations left the club in the Fourth Division by 1962. Crowned Fourth Division champions in 1962–63, Brentford were relegated in 1966 and again in 1973 after gaining promotion in 1971–72. They spent 14 seasons in the Third Division after gaining promotion in 1977–78 and went on to win the Third Division title in 1991–92, though were relegated again in 1993.
Brentford were relegated into the fourth tier in 1998 and won promotion as champions in the 1998–99 campaign. They were relegated in 2007 and won promotion as champions of League Two in 2008–09 and then were promoted out of League One in 2013–14. They had unsuccessful Championship play-off campaigns in 2015 and 2020. Brentford have a poor record in finals, finishing as runners-up in three Associate Members' Cup / Football League Trophy finals (1985, 2001 and 2011) and losing four play-off finals (the 1997 Second Division final, 2002 Second Division final, 2013 League One final and 2020 Championship final). However, Brentford won the 2021 Championship final to be promoted to the highest level for the first time since 1946–47 season.