Evidence of Bronze Age activity in the area is demonstrated by the spectacular Blessington gold lunula, now in the British Museum.

[6] The nearby Rath Turtle Moat was occupied from the 12th century onward by Norse Gaels and Normans.Blessington was previously called Munfine, and in the Medieval period was part of the lordship of Threecastles; Threecastles Castle is a three-storey tower house situated 5 km from Blessington, which was most likely built by Gerald Fitzgerald, Lord Deputy of Ireland, or his son Sir James Fitzgerald.

[13] The Marquess was also responsible for the construction of several prominent buildings in the town such as the Market House (c. 1820), Downshire Lodge (c. 1830), and the Parish schoolhouse (c. 1830).

[12][14] Russborough House, situated 5  km south of Blessington, was built by the Leeson family, Earls of Milltown, and became the home of philanthropist Sir Alfred Beit (1903–1994), before becoming a museum.

During the Irish Civil War, Blessington became a place of strategic importance for the Anti-Treaty forces who regrouped in the town after defeat in Dublin.

Above the nearby village of Lacken in the early hours of 18 April 1941, an RAF Handley Page Hampden aircraft (Registration AD730)[16][17] got lost in bad weather and crashed on Black Hill (Kilbeg)[18] killing its entire crew of four.

The airmen were brought to Blessington and buried with full military funerals on 22 April 1941 at St. Mary's Church by order of the Irish Government.

[17] The Irish Times the day after reported that “During the funeral all shops in Blessington were closed and blinds drawn on windows.”[17] A memorial stone was unveiled at the crash site on 18 April 1991.

[27] Also known locally as the Blessington Lakes, the reservoir was created when the waterfall at Poulaphouca on the River Liffey (which flows from the Wicklow Mountains to Dublin) was dammed by the ESB for a hydroelectric plant which is still in use today.

The lake is also extensively used by boatmen and fishermen, and is a training location for the Irish Air Corps HQ divisions from Baldonnel, 15  km north of Blessington, and also Local Civil Defence Water rescue teams.

[28] The trail starts in Blessington and leads south to The Avon activity centre at the southern edge of the town where it then follows along the lake shore, crossing a medieval ringfort, and uses the footpath along part of the N81 road before turning back into the forest at Burgage Moyle lane.

A second phase for the greenway, laid out in a planning submission by Wicklow County Council in early 2022, is proposed to expand the trail to include a 33  km loop surrounding the lake, taking in the villages of Lacken, Valleymount and Ballyknockan.

Lacking a train station in the town, this service continues to operate as the main public transport connection between Blessington and Dublin city.

The latter starts in the south end of the town heading west and proceeds through a natural gap in the hills of Glending Forest and Eadestown.

[citation needed] Since August 2021, Blessington has been served by route 884, a Mon-Fri public bus service operated by TFI Local Link Kildare South Dublin, which connects the town with Naas and Sallins railway station.