The Liga 3 is the third-level football league in the Portuguese football league system, starting in 2021–22. It is a semiprofessional national league organized by the Portuguese Football Federation (FPF).
The creation of this league is part of a restructuring of the Portuguese third tier, with Campeonato de Portugal, which saw the number of teams reduced, being relegated to fourth tier and the top teams competing there advancing to this new competition. In its first season, a total of 24 teams competed in the Liga 3, 2 of which were relegated from 2020–21 Liga Portugal 2 and 22 others which were promoted from 2020–21 Campeonato de Portugal. This number is set to be reduced to 20 teams from the 2023–24 season.
In the 1990-1991 season, with the creation of the Liga de Honra (second professional division or D2), the Segunda Divisão (Second Division) championship, created in 1934, was relegated to the third division (D3). It was then renamed Segunda Divisão B (Second Division B).
From 1990 to 2005, the championship was divided into 3 groups by geographical division: Norte (North), Centro (Centre) and Sul (South). In 2005, the championship was split into 4 groups: Serie A, Serie B, Serie C and Serie D. But in 2009, the 3-group formula was reinstated.
In 2013, the championship underwent a major reorganisation with the merger with the old Terceira Divisão (Third Division (D4)) and went from 48 to 80 teams. It was renamed the National Senior Championship and took place in the form of eight 10-team series.
In the 2021-22 season, the Portuguese Football Federation created the Liga 3 to replace the former iteration of the third tier of Portugal's football league system (D3) which was at the time the Campeonato de Portugal (from then on D4). Both competitions (D3 and D4) remained two events organised by the federation itself. The Liga 3 was initially contested by 24 clubs in the first two seasons, and in the 2023-2024 season the number of participants was reduced to 20.