Operated as a limited company, the 36 member clubs act as shareholders with one vote each.

The Irish Football League was originally formed as the football league for, in theory, all of Ireland (although, for cultural reasons, all of its member clubs were in fact based in two zones: initially in what would become Northern Ireland, and, from 1900, in Dublin).

St Columb's Court lasted just one season, before being replaced by the league's first Dublin team, Bohemians, in 1902.

In 1911 Glenavon, from the County Armagh town of Lurgan replaced Bohemians, who resigned from the league, but were re-admitted in 1912.

During 1912 there were three Dublin sides, with the addition of Tritonville, but, like Derry Olympic and St Columb's Court before them, they lasted just one season.

Derry Celtic also dropped out in 1913, so that when the Irish League split in 1921, Glenavon was the only non-Belfast team left.

No southern clubs (from what would become the Irish Free State and later the Republic of Ireland) ever won the championship.

During the 1920s, however, the league expanded and soon achieved a wide geographic spread across Northern Ireland.

Nonetheless, no club from outside Belfast won the League championship for the first 62 years of its existence, until Glenavon took it to County Armagh in 1951–52.

While some of these once enjoyed considerable prestige, they have been phased out over the years due to fixture congestion caused by the expansion of the league, and reduced spectator interest.

The first ever Irish League match to be broadcast live on television took place on 24 September 2007 when Sky Sports showed Cliftonville and Linfield draw 2–2 at Solitude.

Ten of the 12 clubs succeeded in meeting the necessary standard in 2009 and the Championship was then divided into two divisions.

Belfast Celtic won five consecutive titles between 1935–36 and 1939–40, before the suspension of the league in 1940 due to World War II.

On the resumption of the league in 1947–48 they won their sixth consecutive title, albeit eight years after the fifth.

A total of 12 different clubs have won the championship, Linfield holding the record for the most wins (56).

In the 1905–06 season, the championship title was shared after Cliftonville and Distillery could not be separated after two play-off matches.

Before goal difference was introduced, if the top two teams finished the season with the same number of points, the championship title was decided by a play-off.

Nine such championship play-offs took place over the years as follows: On seven occasions, a team has completed a league campaign unbeaten.

Linfield have done so four times, but with fewer fixtures relative to Belfast Celtic's unbeaten seasons in 1926–27 and 1928–29.

That was the second consecutive season that a new member club had made its first appearance in the league, following Ballinamallard United's debut a year earlier in 2012.

Prior to the split, three southern clubs had participated in the League: Bohemians, Shelbourne and Tritonville.

When the League resumed in 1947 it was reduced to twelve clubs, and stayed at this number until 1983 when membership was increased to fourteen.

Listed below are all the senior League members from 1890 up to and including the 2024–25 season in the following competitions: Bold – a current member Italics – a club no longer in existence, or no longer competing in Northern Irish football Between 1995–96 and 2002–03, the league was split into two divisions, with promotion and relegation between the two as follows.

It was discontinued after 2002, but a new IFA Intermediate League Cup was played between 2004 and 2008, sponsored in its first season by the Daily Mirror and thereafter by Carnegie.