During 1st Phase of the 2025-2026 WAL1 regular season, each WAL1 team plays each other 11 WAL1 teams twice for a total of 22 league matches. In the 2nd Phase, the top six teams play in the Championship Group and the bottom 6 teams play in the Relegation Group. Each team plays Home-Away matches against the other 5 teams in their group (10 more matches, 32 matches total) to determine final rankings for 2026-2027 UEFA Champions League, Europa League placements, and relegation. Table rankings ties are broken by (1) goal difference, (2) goals scored, (3) head-to-head goal difference, (4) head-to-head goals scored, (5) head-to-head Away goals scored, (6) matches won, then (7) Away matches won.

At the end of the 2025-2026 WAL1 regular season, the 3rd through 6th place WAL1 Championship Round teams and the 1st place WAL1 Relegation Round team have a European Competition playoff. The playoff winner receives a a berth in the Preliminary Round of the 2026-2027 UEFA Europa Conference League. (If the winner of the 2025-2026 Welsh Cup has already received a berth in the Champions League or the Europa League, the other playoff Finalist receives this berth.)

At the end of the 2025-2026 WAL1 regular season, the 5th and 6th place WAL1 Relegation Round teams will be relegated to either the WAL2A or WAL2B, and the top 2 teams in the WAL2A/2B are promoted to the 2026-2027 WAL1.