The season began on 19 August 2017 and ended on 27 May 2018.
[1] The 2017–18 Slovenian Third League was divided into four regional groups with a total of 50 participating clubs.
The three groups (North, Centre, East) were composed of 14 clubs, while the West group consisted of 8 clubs.
The winners of the regular season in each group played a promotional two-legged play-off to decide the two teams promoting to the Slovenian Second League.
A two-legged play-offs between the group winners for promotion to the 2018–19 Slovenian Second League.