The 2017 Thai League T1 (also known as the Toyota Thai League for sponsorship reasons) was the 21st season of the Thai League, the top Thai professional league for association football clubs, since its establishment in 1996. A total of 18 teams will compete in the league. The season began on 11 February 2017. Fixtures for the 2017 season were announced on 12 January 2017.
Muangthong United are the defending champions, having won the Thai Premier League title the previous season. Thai Honda Ladkrabang, Ubon UMT United and Port have entered as the three promoted teams from the 2016 Thai League 2.
There are 18 clubs in the league, with three promoted teams from Thai League 2 replacing the three teams that were relegated from Thai League T1 following the 2016 season. All clubs that secured Thai League status for the season were subject to approval by the AFC Club Licensing before becoming eligible to participate.
Army United, Chainat Hornbill and BBCU were relegated at the end of the 2016 season after finishing in the bottom three places of the table. They were replaced by 2016 Thai League 2 champions Thai Honda Ladkrabang, 2nd place Ubon UMT United and 3rd place Port, were promoted to bring the total teams in the league to 18.
Ubon UMT United was founded in 2015, they finishing as Thai League 2 runners up in 2016, and earned promotion to the Thai League T1 for the first time in their history.
Note: Flags indicate national team as has been defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality.
The number of foreign players is restricted to five per T1 team. A team can use four foreign players on the field in each game, including at least one player from the AFC member countries (3+1).
<onlyinclude></onlyinclude>
Source: Thai League<br /> Note:<br /> Attendances on the match SCG Muangthong United vs. Port (17 May 2017) had banned by FA Thailand.<br /> Attendances on the match Port vs. SCG Muangthong United (22 October 2017) had banned by FA Thailand.