Work commenced in 1790 and lasted 27 years before finally reaching the Shannon in 1817, at a total cost of £1,421,954 . The canal passes through Maynooth, Kilcock, Enfield, Mullingar and Ballymahon has a spur to Longford. The total length of the main navigation is 145 kilometres (90 mi), and the system has 46 locks. There is one main feeder (from Lough Owel), which enters the canal at Mullingar. At the Dublin end, the canal reaches the Liffey through a wide sequence of dock and locks at Spencer Dock, with a final sea lock to manage access to the river and sea.
In 1843, while walking with his wife along the Royal Canal, Sir William Rowan Hamilton realised the formula for quaternions and carved his initial thoughts into a stone on the Brougham Bridge over the canal.The Dublin - Mullingar railway line was built alongside the canal for much of the distance. The meandering route of the canal ensures a speed limiting curvature for the railway.
The canal travels across one of the major junctions on the M50/N3 in a specially constructed aqueduct.By the 1970s the canal was falling into total disrepair and became a dumping ground for old cars and rubbish. Suggestions were made the inner Dublin part of the canal to become motorway which lead to the community forming an action group to encourage the Dublin City Council to clean and maintain the canal.
Waterways Ireland is now responsible for the canal. The full canal between the Liffey in Dublin and the Shannon in Co. Longford reopened on the 2nd of October 2010. Access points currently exist near Leixlip and at Maynooth, Enfield, Thomastown, Mullingar, Ballinea Bridge and Ballynacargy.
In 2006 a commemoration marker was erected at Piper's Boreen, Mullingar, to mark the 200 years since the canal reached Mullingar in 1806.