| Club: | Dumbarton |
| Season: | 2009-10 |
| Manager: | Jim Chapman |
| Stadium: | Strathclyde Homes Stadium, Dumbarton |
| League: | Scottish League Division 2 |
| League Result: | 6th |
| Cup1 Result: | Third Round |
| Cup2 Result: | First Round |
| Cup3 Result: | First Round |
| Matches: | 40 |
| Total Goals: | 49 |
| League Topscorer: | Scott Chaplain (10) |
| Season Topscorer: | Scott Chaplain (10) |
| Highest Attendance: | 975 |
| Lowest Attendance: | 397 |
| Average Attendance: | 681 |
| Prevseason: | 2008–09 |
| Nextseason: | 2010–11 |
Season 2009–10 was the 126th football season in which Dumbarton competed at a Scottish national level, entering the Scottish Football League for the 104th time, the Scottish Cup for the 115th time, the Scottish League Cup for the 63rd time and the Scottish Challenge Cup for the 19th time.
Following the success of the previous season, it was manager Jim Chapman's goal to consolidate the club's position in the Second Division. However, Dumbarton were to be devastated before a ball was kicked with the death during the close season of the club captain, Gordon Lennon, from a motoring accident. Nevertheless, despite there being few changes to the playing staff, the league campaign started disappointingly with only two draws to show from the first six starts - resulting in the club propping up the rest of the league. It was, however, to be a temporary blip and although there was no consistency in performances, a mid-table sixth place was achieved in the end.
In the domestic cups, however, it was all bad news - no wins and no goals! In the Scottish Cup, local rivals Morton would be victorious in the third round, after a goalless draw. In the League Cup, Dunfermline Athletic had no difficulty in seeing off Dumbarton in the first round.
Finally, it was no surprise that the League Challenge Cup would witness another first round exit, and it would be Morton again who would do the damage.
Locally, the Stirlingshire Cup was resumed, and after two penalty shoot out wins in the group fixtures, the trophy would return to Dumbarton following a win in the final over Stenhousemuir.
See main article: 2009–10 Scottish Second Division.
See main article: 2009–10 Scottish Challenge Cup.
See main article: 2009–10 Scottish League Cup.
See main article: 2009–10 Scottish Cup.
- won on penalties
|}
| Player | From | Date | |
|---|---|---|---|
| Ross O'Donoghue | Elgin City | 22 Jun 2009 | |
| Scott Chaplain | Partick Thistle | 30 Jun 2009 | |
| Roddy Hunter | Montrose | 14 Jul 2009 | |
| Denis McLaughlin | Hearts (loan) | 24 Jul 2009 | |
| Chris Craig | Rangers | 4 Aug 2009 | |
| Chris Smith | Morton | 4 Aug 2009 | |
| Simon Lynch | Airdrie United (loan) | 15 Aug 2009 | |
| Ross Harvey | Rangers | 28 Aug 2009 | |
 Jan Vojacek | SK Sigma Olomouc | 28 Aug 2009 | |
| Adam Strachan | Albion Rovers | 18 Sep 2009 | |
| Dennis Wyness | St Mirren | 11 Feb 2010 | |
| David Winters | Arbroath | 12 Mar 2010 |
| Player | To | Date | |
|---|---|---|---|
| Michael O'Byrne | Albion Rovers | 2 Jun 2009 | |
| Mark Canning | Albion Rovers | 3 Jun 2009 | |
| Fergus Tiernan | Queen's Park | 1 Jul 2009 | |
| Pat Boyle | Partick Thistle | 10 Jul 2009 | |
| Paul Keegan | Airdrie United | 22 Jul 2009 | |
| Paul McLeod | Clyde | 22 Jul 2009 | |
| David McFarlane | Albion Rovers | 23 Jul 2009 | |
| Mark McGeown | Queen of the South | 16 Oct 2009 | |
| Adam Strachan | Clyde | 13 Nov 2009 | |
| Nathan Taylor | Clitheroe | 1 Jan 2010 | |
| Paul Craig | Freed | 25 Mar 2010 | |
| Chris Craig | Alloa Athletic | 1 Apr 2010 | |
| Ross Harvey |  Embry Riddle Eagles | ||
| Gary Wilson | Larkhall Thistle | ||
| Dave McEwan | Beith |