The Ulster Senior League is a rugby union competition for senior clubs in the Irish province of Ulster. It was formed by the then Northern Branch of the Irish Rugby Football Union in October 1890. It has traditionally being ranked second in importance to the Ulster Senior Cup. It has declined in importance due to the formation of the All-Ireland League and growth in importance of the Heineken Cup.
The Senior League has had a chequered history. Its value was marred in the amateur era by periods when the elite clubs like North, Instonians and Collegians withdrew from the league to allow them to fulfil more friendly fixtures - particularly against English and Welsh opposition. This attitude from some of the senior clubs even lead to the scrapping of the league in 1930, and it was not re-established until after World War II. The practice of withdrawing from the league finally died out in the 1970s.
Mostly the league was played in one section on an all-play-all home and away basis. However, with the expansion of the number of Senior Clubs in 1980, two sections were formed and the top two teams qualified for semi-finals. This allowed for a showpiece final at the end of the season.
The two section arrangement continued until 1990 when the advent of professionalism and preparation for the All-Ireland League, saw the league separated into two sections based on playing ability. Promotion and relegation between the two sections was introduced at this time. This later gave way to a single-division league.
From the 2015-16 season, the League was renamed as the Ulster Championship League and divided into two sections (Division 1 and Division 2), with promotion and relegation between the two. The league was renamed the Soni Premiership in 2016-17.
The winners receive the Stevenson Shield.