The cemetery contains historically notable monuments and the graves of many of Ireland's most prominent national figures. These include the graves of Daniel O'Connell, Charles Stewart Parnell, Michael Collins, Éamon de Valera, Arthur Griffith, Maude Gonne, Kevin Barry, Roger Casement, Constance Markievicz, Pádraig Ó Domhnaill, Seán MacBride, Jeremiah O'Donovan Rossa, James Larkin, Brendan Behan, Christy Brown and Luke Kelly of the Dubliners.
The grave of Michael Collins, the nationalist leader who was killed in the Irish Civil War in 1922, is among the most visited sites in Glasnevin. Around him were buried at least 183 soldiers of the Irish Free State. In 1967 their names were recorded on memorial around Collin's grave.
In 1993 a mass grave at the site of a Magdalene laundry, institutions ostensibly used to house "fallen women", was discovered after the convent which ran the laundry sold the land to a property developer. The Sisters from the Convent arranged to have the remains cremated and reburied in a mass grave at Glasnevin Cemetery, splitting the cost of the reburial with the developer who had bought the land.
The cemetery also offers a view of the changing style of death monuments in Ireland over the last 200 years: from the austere, simple, high stone erections of the period up until the 1860s, to the elaborate Celtic crosses of the nationalistic revival from the 1860s to the 1960s, to the plain Italian marble of the late 20th century.
The high wall with watch-towers surrounding the main part of the cemetery was built to deter bodysnatchers, who were active in Dublin in the 18th and early 19th centuries. The watchmen also had a pack of blood-hounds who roamed the cemetery at night.
In 2009, Glasnevin Trust in co-operation with the Commonwealth War Graves Commission (CWGC) began identifying the graves of Irish service personnel who died while serving in the Commonwealth forces during the two world wars. These names are inscribed on two memorials, rededicated and relocated in 2011 to near the main entrance. A Cross of Sacrifice was erected in the cemetery, in a joint Irish-British commemoration ceremony, to mark the First World War centenary. As of July 2019, there are 215 service personnel of the Commonwealth of both wars identified as buried here.