The 1920–21 season was Burnley's 29th season in the Football League, and their 4th consecutive campaign in the Football League First Division, the top tier of English football. Burnley were confident of success ahead of the season, having finished as First Division runners-up in 1919–20. After losing their first three games, Burnley embarked on a 30-match unbeaten league run from 4 September 1920 until 26 March 1921, winning the First Division and becoming English champions for the first time in their history. Burnley's unbeaten run stood as a single-season Football League record for over 80 years, until it was bettered by Arsenal in the 2003–04 season. Burnley ended the 1920–21 season on 59 points, having won 23 games, drawn 13, and lost 6.

Burnley Football Club are a football club in Burnley, Lancashire, England. They compete in the Premier League, the first tier of English football, but will compete in the 2024–25 EFL Championship following relegation. Founded in 1882, the club was one of the first to become professional and subsequently put pressure on the Football Association to permit payments to players. The club entered the FA Cup for the first time in 1885–86 and was one of the 12 founder members of the Football League in 1888–89. From the 1950s until the 1970s, under chairman Bob Lord, the club became renowned for its youth policy and scouting system, and was one of the first to set up a purpose-built training ground.