| Club: | Chelsea |
| Season: | 1939–40 |
| Manager: | Billy Birrell |
| Chairman: | Lt. Col Charles Chrisp |
| Stadium: | Stamford Bridge |
| League: | First Division |
| League Result: | 8th |
| Cup1: | Football League War Cup |
| Cup1 Result: | First round |
| Pattern B1: | _chelsea1907h |
| Pattern So1: | _2bluestripes |
| Leftarm1: | 0000FF |
| Body1: | FFFFFF |
| Rightarm1: | 0000FF |
| Shorts1: | ffffFF |
| Socks1: | 000000 |
| Pattern So2: | _2bluestripes |
| Leftarm2: | FF0000 |
| Body2: | FF0000 |
| Rightarm2: | FF0000 |
| Shorts2: | FFFFFF |
| Socks2: | 000000 |
| Prevseason: | 1938–39 |
| Nextseason: | 1940–41 |
The 1939–40 season was Chelsea Football Club's thirty-first competitive season. The Football League season was abandoned after three matches due to the outbreak of the Second World War and the FA Cup was not contested. For the next six years, the club instead competed in unofficial regional leagues, which are not considered competitive. Chelsea finished 3rd in League South B and subsequently finished 9th in an additional competition, League South C