| Club: | Millwall |
| Manager: | Kenny Jackett |
| Nextseason: | 2009–10 |
| Season: | 2008–09 |
| Prevseason: | 2007–08 |
| League Result: | 5th |
| League: | League One |
| Season Topscorer: | Gary Alexander (11) |
| League Topscorer: | Gary Alexander (9) |
| Season Top Appearances: | David Forde (51) |
| League Top Appearances: | David Forde (44) |
| Chairman: | John Berylson |
| Cup1: | FA Cup |
| Cup1 Result: | Fourth round |
| Cup2: | League Cup |
| Cup2 Result: | First round |
| Cup3: | EFL Trophy |
| Cup3 Result: | First round |
| Highest Attendance: | 13,261 (vs Leicester, 14 March 2009) |
| Lowest Attendance: | 6,685 (vs Northampton, 10 March 2009) |
This article details Millwall's 2008–09 season in League One, Millwall's 83rd season in the Football League and 40th in the third tier.
This will be a list of the significant events to occur at the club during the 2008–09 season, presented in chronological order.
9 August 2009- season begins with a 4–3 loss at Oldham.
12 August 2009- Knocked out in the first round of the League Cup at home to Northampton.
Appearances (starts and substitute appearances) and goals include those in the League One (and playoffs), FA Cup, League Cup and EFL Trophy.