| Temporada | Equipo | Competición | PJ | G | A | Nota | ||
|---|---|---|---|---|---|---|---|---|
| 2026 | Dundalk | Premier Division | 5 | 1 | 0 | 1 | 0 | 6.5 |
| 2025 | Derry City | Premier Division | 18 | 5 | 0 | 6 | 1 | 6.9 |
| 2024 | Derry City | Premier Division | 19 | 4 | 1 | 2 | 0 | 6.9 |
| 2023 | Derry City | Premier Division | 3 | 0 | 0 | 0 | 0 | 6.7 |
| 2022/2023 | Partick Thistle | Premiership | 5 | 1 | 0 | 0 | 0 | – |
| 2022/2023 | Partick Thistle | Championship | 26 | 4 | 1 | 0 | 0 | – |
| 2021/2022 | Dundee FC | Premiership | 25 | 7 | 1 | 6 | 0 | 6.7 |
| 2020/2021 | Dundee FC | Premiership | 4 | 1 | 0 | 0 | 0 | – |
| 2020/2021 | Dundee FC | Championship | 25 | 5 | 2 | 2 | 0 | – |
| 2019/2020 | St. Mirren | Premiership | 10 | 2 | 0 | 1 | 0 | 6.7 |
| 2018/2019 | St. Mirren | Premiership | 25 | 6 | 0 | 3 | 0 | – |
| 2017/2018 | St. Mirren | Championship | 19 | 3 | 0 | 2 | 0 | – |
| 2017/2018 | Livingston | Championship | 11 | 4 | 0 | 7 | 0 | – |
| 2016/2017 | Livingston | League One | 32 | 14 | 0 | 4 | 0 | – |
| 2015/2016 | Livingston | Championship | 21 | 2 | 0 | 1 | 0 | – |
| 2014/2015 | Livingston | Championship | 32 | 10 | 0 | 4 | 0 | – |
| 2013/2014 | Livingston | Championship | 23 | 2 | 0 | 1 | 0 | – |
| 2012/2013 | Livingston | Division 1 | 6 | 2 | 0 | 0 | 0 | – |
| Total | 309 | 73 | 5 | 40 | 1 | – | ||
| Fecha | Desde | Hacia | Tipo | |
|---|---|---|---|---|
| 01 feb 2026 | Derry City | Dundalk | Free agent | |
| 07 jun 2023 | Partick Thistle | Derry City | Free agent | |
| - | Dundee FC | Partick Thistle | Free agent | |
| 08 abr 2020 | St. Mirren | Dundee FC | Free agent | |
| 01 nov 2018 | Livingston | St. Mirren | Transfer | |
| 01 oct 2018 | St. Mirren | Livingston | Return from loan | |
| 12 dic 2017 | Livingston | St. Mirren | Loan | |
| 07 ene 2012 | Aberdeen | Livingston | Free agent |
D. Mullen career history shows progression across clubs and competitions, including club timeline, national team appearances and overall career totals.