| Season: | 2018 |
| Relegated: | Kalasin (Upper Region) Deffo (Lower Region) |
| League Topscorer: |  Chatchai Narkwijit(20 Goals) |
| Biggest Home Win: | 7 goals difference (5 August 2018) |
| Biggest Away Win: | 5 goals difference (7 July 2018) |
| Highest Scoring: | 8 goals (26 August 2018) |
| Matches: | 368 |
| Total Goals: | 919 |
| Longest Wins: | 6 matches JL Chiangmai United (2 matches from final) |
| Longest Unbeaten: | 23 matches JL Chiangmai United (2 matches from final) |
| Highest Attendance: | 3,116 (19 August 2018) |
| Lowest Attendance: | 30 (30 June 2018) (28 July 2018) |
| Attendance: | 146,747 |
| Average Attendance: | 401 |
| Nextseason: | 2019 |
The 2018 Thai League 3 (known as the Omsin League Pro for sponsorship reasons) football season will be the second season of Thai League 3. 31 clubs will be divided into 2 groups (regions).
Promoted to the 2018 Thai League 2
Promoted from the 2017 Thai League 4
Relegated to the 2018 Thai League 4 Northern Region
Relegated to the 2018 Thai League 4 Western Region
Relegated from the 2017 Thai League 2
| Team | Location | Stadium | Capacity | |
|---|---|---|---|---|
| Ayutthaya | Ayutthaya | Udhomseelwitthaya School Stadium | 1,800 | |
| Ayutthaya United | Ayutthaya | Ayutthaya Provincial Stadium | 6,000 | |
| Bangkok | Bangkok | Bang Mod Honorary Stadium | 8,000 | |
| Chachoengsao | Chachoengsao | Chachoengsao Municipality Stadium | 6,000 | |
| Chiangrai City | Chiang Rai | Chiangrai Province Stadium | 5,000 | |
| Kalasin | Kalasin | Kalasin Municipality Stadium | 2,580 | |
| Kamphaengphet | Kamphaengphet | Cha Kung Rao Stadium | 2,406 | |
| JL Chiangmai United | Chiang Mai | 700th Anniversary Stadium | 25,000 | |
| Lamphun Warrior | Lamphun | Mae-Guang Stadium | 3,000 | |
| Marines Eureka | Rayong | Klaeng Municipality Stadium | 1,661 | |
| Muangkan United | Kanchanaburi | Kleebbua Stadium | 5,403 | |
| Phrae United | Phrae | Thunghong Municipality Stadium | 4,500 | |
| Sakaeo | Sakaeo PAO. Stadium | 10,000 | ||
| Ubon Ratchathani | Ubon Ratchathani University Stadium | 2,000 |
| Team | Location | Stadium | Capacity |
|---|---|---|---|
| BTU United | Bangkok | Bangkok-Thonburi University Stadium | 1,500 |
| Chamchuri United | Bangkok | Chulalongkorn University Stadium | 20,000 |
| Deffo | Bangkok | TOT Stadium Chaeng Watthana | 5,000 |
| Kasem Bundit University | Bangkok | Kasem Bundit University Stadium, Rom Klao | 2,000 |
| MOF Customs United | Samut Prakan | Customs Department Stadium, Ladkrabang 54 | 2,000 |
| Nara United | Narathiwat | Narathiwat PAO. Stadium | 5,000 |
| Phuket City | Phuket | Surakul Stadium | 15,000 |
| Rajpracha | Bangkok | Thonburi Stadium | 5,000 |
| Ranong United | Ranong | Ranong Provincial Stadium | 7,000 |
| Royal Thai Army | Bangkok | Thai Army Sports Stadium | 20,000 |
| Angthong | Angthong Provincial Stadium | 6,000 | |
| Surat Thani | Surat Thani Provincial Stadium | 10,000 | |
| Trang | Trang Municipality Stadium | 5,000 | |
| WU Nakhon Si United | Nakhon Si Thammarat | Walailak University Stadium | 10,000 |
See main article: 2018 Thai League 3 Upper Region.
See main article: 2018 Thai League 3 Lower Region.
This round was featured by Ayutthaya United, the second place of 2018 Thai League 3 Upper Region and Nara United, the second place of 2018 Thai League 3 Lower Region. Winners of third place play-off would promoted to 2019 Thai League 2.
Ayutthaya United won 2–1 on aggregate.
This round was featured by JL Chiangmai United, the first place of 2018 Thai League 3 Upper Region and MOF Customs United, the first place of 2018 Thai League 3 Lower Region. Both winners and runners-up would promoted to 2019 Thai League 2 automatically.
JL Chiangmai United won 2–0 on aggregate.