The Leinster Senior League Senior Division is the top division of the Leinster Senior League. It is organized by the Leinster Football Association. Together with the Munster Senior League Senior Premier Division and the Ulster Senior League Senior Division, it forms the third level of the Republic of Ireland football league system. Formed in 1896, it is the oldest association football league in what is now the Republic of Ireland. Shelbourne have won the most titles. However, in more recent seasons Crumlin United, Cherry Orchard, Wayside Celtic and Bangor Celtic have been the divisions strongest teams. In 2014–15 Bluebell United were Leinster Senior League champions, 27 years after winning their previous title. Clubs from this division play in the Leinster Senior Cup, the FAI Cup, the FAI Intermediate Cup and the FAI Junior Cup. In recent seasons the winners of the Senior Division have also been invited to play in the League of Ireland Cup.
From 1896–97 until 1964–65 the league was the de facto second level league in what is now the Republic of Ireland. Initially the Irish Football League was the top level. Then for one season, 1920–21, the Leinster Senior League was briefly the top level league. However this status was short lived and ended with the establishment of the League of Ireland in 1921–22. The Leinster Senior League remained a second level league until 1964–65 when it was effectively replaced by the League of Ireland B Division. With the establishment of the A Championship in 2008 it became a fourth level league. However, since the demise of the A Championship in 2011, it has reverted to third level status.